Homemade Cream of Mushroom and Onion Soup

Homemade Cream of Mushroom and Onion Soup is a rich, creamy, make-ahead recipe made with finely chopped mushrooms, sweet Vidalia onions, Boursin cheese, and heavy cream. A simple cornstarch slurry gives this homemade soup the right amount of body without a traditional flour-based roux!

It’s perfect for chicken casseroles, green bean casserole, and all those cozy Thanksgiving dishes you want to prepare ahead of time.

Here’s something you should know about me: I don’t like mushrooms.

I know! But I LOVE the flavor of mushrooms. I can’t get past the big, squishy mushroom pieces.

So, when I make my homemade Cream of Mushroom and Onion Soup, I chop those mushrooms as finely as possible. Almost the same size as my diced onions.

All that wonderful mushroom flavor, none of those giant mushroom chunks.

And y’all, this soup is GOOD.

It’s rich, creamy, filled with sweet Vidalia onions, and has a whole wheel of Shallot & Chive Boursin cheese melted right into it.

Best of all? It makes two quarts, which means you can use some now and freeze some for later.

Future You Approves!

Why You’ll Love This Homemade Cream Soup

If you’ve been reaching for canned cream of mushroom soup every time you make a casserole, meet your new favorite homemade version.

• No flour or roux required. A simple cornstarch slurry helps thicken the soup without the extra step of making a traditional roux. The butter, heavy cream, and Boursin cheese give it that wonderfully rich, creamy finish.
• Simple ingredients. Just mushrooms, onion, butter, cheese, cream, salt, and pepper.
• Make it ahead. Prepare a batch now and freeze portions for future recipes.
• Perfect for casseroles. Use it as a creamy base for green bean casserole, chicken casseroles, and other comfort food favorites.
• No big mushroom pieces. Finely chopping the mushrooms gives you all the flavor without the texture.

This recipe makes me feel like I’ve done something really kind for Future Me.

And that’s what my Holiday Headquarters is all about!

Ingredients for Homemade Cream of Mushroom and Onion Soup

You only need a handful of simple ingredients to make this homemade cream of mushroom and onion soup!

Button Mushrooms: One 8-ounce carton of white button mushrooms. I wipe mine clean with a damp paper towel before chopping them very finely.

Butter: One whole stick! This is homemade Southern comfort food, baby. The butter helps soften the onions and gives the soup a rich flavor.

Vidalia Onion: One large sweet Vidalia onion, finely diced. I love the gentle sweetness of Vidalia onions, especially paired with mushrooms.

Boursin Shallot & Chive Cheese: One whole 5.2-ounce wheel. This adds creamy texture and wonderful shallot and herb flavor.

Heavy Whipping Cream: One quart (4 cups). This is what makes the soup so luscious.

Cornstarch: Just one tablespoon! This helps thicken the soup without using flour or making a traditional roux.

Cold Water: Half a cup of cold water mixed with the cornstarch creates a smooth slurry that blends right into the soup without lumps.

Kosher Salt and Black Pepper: Season to taste.

That’s it!

How to Make Cream of Mushroom and Onion Soup

Step 1: Finely Chop the Mushrooms

Start by wiping your mushrooms clean with a damp paper towel.

Then chop them finely.

And when I say finely, I mean FINELY.

I want my mushrooms to be about the same size as my diced onions. That way, you get all the wonderful flavor without biting into big mushroom pieces.

Step 2: Cook the Mushrooms in a Dry Pan

Here’s my favorite trick!

Add your chopped mushrooms to a DRY pan over medium heat.

No butter. No oil. Nothing.

Mushrooms contain a lot of water, and I like to cook them until they release that moisture and it evaporates.

Keep cooking until the mushrooms start to sound and feel almost squeaky as you stir them around the pan.

That’s when I know they’re ready for the next step!

I use my Made In Saucier Pan for this recipe. It’s one of those pieces of cookware I reach for constantly.

Step 3: Add Butter and Sweet Vidalia Onion

Once your mushrooms have released their moisture, add one stick of butter and your finely diced Vidalia onion.

Stir everything together and cook over medium heat until the onions soften and become translucent.

You aren’t trying to caramelize the onions here. You just want them tender and sweet.

Step 4: Add Heavy Cream and Boursin

Season the mushroom-and-onion mixture with kosher salt and freshly ground black pepper.

Pour in one quart of heavy whipping cream.

Then add one entire wheel of Shallot & Chive Boursin cheese.

Reduce the heat to medium-low and stir gently until the Boursin melts into the cream.

Let everything warm through until it’s smooth, rich, and creamy.

You don’t need a rolling boil!

Boursin cheese softening in a creamy mushroom and onion soup mixture

Step 5: Thicken the Soup with a Cornstarch Slurry

Here’s how we give our homemade cream soup a little extra body!

In a small bowl, whisk together one tablespoon of cornstarch and half a cup of COLD water.

And yes, that water needs to be cold! Mixing cornstarch with cold liquid helps it dissolve evenly before adding it to the hot soup.

Slowly pour the slurry into your soup while whisking everything together.

Bring the soup to a gentle simmer and let it cook for another minute or two, stirring occasionally, until it thickens slightly.

You’re looking for a rich, creamy, pourable soup. Not something quite as thick as condensed canned soup, but thick enough to make a wonderful casserole base.

And that’s it, y’all!

Step 6: Cool, Store, or Use!

And just like that, you’ve made homemade Cream of Mushroom and Onion Soup!

This recipe makes approximately two quarts.

Use it right away in your favorite casserole, refrigerate it for another day, or freeze portions to make future dinners easier.

My Best Tips for Homemade Cream Soup

Cook the Mushrooms Before Adding Butter

I know it sounds unusual, but starting mushrooms in a dry pan is one of my favorite cooking techniques.

Mushrooms contain quite a bit of water. When you add them to a dry pan, they begin releasing that moisture.

I like to cook until most of that liquid evaporates before adding my butter.

This concentrates the mushroom flavor and keeps all that extra water from going into the cream sauce.

Chop Everything Small

This is especially important if you’re like me and don’t love the texture of mushrooms.

Finely chopped mushrooms and onions blend together beautifully.

You still get the wonderful savory flavor, but without those big mushroom chunks.

Use Sweet Onions

Vidalia onions are my favorite for this recipe.

Their natural sweetness works so well with the earthy mushrooms and savory Boursin cheese.

If you can’t find Vidalias, another sweet onion variety will work.

Don’t Skip the Boursin!

That Shallot & Chive Boursin cheese adds so much flavor!

It’s one of those shortcut ingredients that makes a simple recipe taste like you’ve been standing over the stove all afternoon.

Season at the End, Too

Taste the finished soup before adding more salt.

Boursin already brings seasoning to the party, so you may not need as much salt as you think.

Can You Freeze Homemade Cream of Mushroom and Onion Soup?

YES!

Now, I know what people say about freezing heavy cream.

And technically, they’re right that cream-based sauces can separate after freezing and reheating.

But y’all, I’ve frozen this soup several times and have never had a problem I couldn’t fix!

Here’s how I do it:

1. Let the finished soup cool before transferring it to freezer-safe containers.
2. Portion the soup according to how you plan to use it.
3. Leave room for expansion in the containers.
4. Label each container with the name and date.
5. Freeze until you’re ready to use it.

When you’re ready to cook, thaw the soup in the refrigerator and reheat gently over low heat.

Here’s my little trick if the cream separates:

Add a few tablespoons of boiling water and whisk vigorously until the sauce comes back together.

It has worked beautifully for me!

For the best quality, I recommend using frozen portions within two to three months.

And a little reminder: If you’re freezing in glass jars, make sure they’re specifically freezer-safe, leave the recommended headspace, and don’t put hot soup directly into cold glass.

A note about freezing cornstarch-thickened soup: Sometimes, cornstarch-thickened sauces can change consistency after freezing and thawing. I’ve had wonderful luck freezing this homemade soup, but if yours separates or looks a little different when you reheat it, don’t panic! Warm it gently and give it a good whisk. If needed, add a tablespoon or two of boiling water to help bring everything back together.

How to Thicken Cream of Mushroom Soup Without Flour

You don’t need flour or a traditional roux to make homemade cream of mushroom soup!

For this recipe, I use a simple cornstarch slurry to give the soup a little extra body.

A cornstarch slurry is just cornstarch mixed with cold liquid before it’s added to something hot.

For my homemade Cream of Mushroom and Onion Soup, I mix one tablespoon of cornstarch with half a cup of cold water.

Once the Boursin cheese has melted into the heavy cream, I whisk in the slurry and let everything gently simmer until it thickens.

My biggest tip? Always mix your cornstarch with cold water first!

Adding dry cornstarch directly to hot soup can create lumps, and nobody wants that.

The result is a rich, creamy homemade mushroom soup that’s perfect for casseroles, chicken bakes, and make-ahead holiday cooking.

And because we’re only using one tablespoon of cornstarch for the entire batch, the soup stays beautifully pourable instead of becoming overly thick.

How to Use Homemade Cream of Mushroom and Onion Soup

This is where the magic happens!

I don’t necessarily make this soup to eat a big bowl of it. I make it because it’s a wonderful creamy base for some of my favorite comfort food recipes.

Green Bean Casserole: Use it in place of canned cream of mushroom soup for a rich, homemade Thanksgiving side dish. I’ve started using this soup in place of the store-bought canned version in my Green Bean Casserole recipe!

Chicken Casseroles: Spoon this creamy mushroom and onion mixture over chicken before baking.

Creamy Rice Dishes: Stir some into cooked rice for an easy, comforting side dish.

Pork Chops: Use it as the base of a creamy sauce for baked pork chops.

Vegetable Casseroles: Try it with broccoli, cauliflower, or other vegetables that need a little creamy goodness.

Because this homemade version isn’t as concentrated as canned condensed soup, start with a similar volume and adjust the other liquid in your recipe as needed.

Make Thanksgiving Easier with Homemade Cream Soup

If you’re following along with my Holiday Headquarters series, you already know how much I love preparing things ahead of time.

And this is exactly the kind of recipe I want you making in October!

Think about all the casseroles you’ll prepare for Thanksgiving.

What if the creamy base was already made?

What if you could pull a container of homemade cream of mushroom and onion soup out of your freezer, thaw it, and have one less thing to do?

That’s what I call making November merrily mundane.

You don’t have to prepare the entire Thanksgiving dinner in one day.

You can do little things now that make the holiday season easier later.

Host Yourself First, baby.

Frequently Asked Questions

Can I substitute regular onions for Vidalia onions?

Yes! Any sweet onion is a good substitute. Yellow onions will also work, although the finished soup may have a slightly sharper onion flavor.

Can I use baby bella mushrooms instead?

Yes. Baby bella mushrooms have a deeper, earthier flavor than white button mushrooms. Either variety will work in this recipe.

Can I make cream of mushroom soup without flour?

Absolutely! This homemade cream of mushroom and onion soup uses heavy cream, Boursin cheese, and a simple cornstarch slurry to create a rich, creamy consistency without flour or a traditional roux.

Is this the same as condensed cream of mushroom soup?

Not exactly! This homemade version is creamy and slightly thickened with cornstarch, but it isn’t as concentrated as canned condensed cream of mushroom soup. When using it in casserole recipes, you may need to adjust the amount of additional liquid.

Can I use a different flavor of Boursin?

Yes! Garlic & Fine Herbs would be a delicious alternative, although Shallot & Chive is the flavor I use in my original recipe.

How long does homemade cream of mushroom soup last in the refrigerator?

Store it in an airtight container in the refrigerator for three to four days.

Can I freeze soup made with heavy whipping cream?

Yes, although the texture may change after thawing. Reheat gently, whisk well, and add a small amount of hot water if needed to help bring the sauce back together.

How much homemade cream of mushroom soup equals one can?

A standard 10.5-ounce can of condensed cream of mushroom soup contains approximately 1¼ cups. However, this homemade version is creamier and more pourable than condensed soup, so it isn’t an exact substitute.

Start with about 1¼ cups of homemade soup for each can called for in your recipe, then reduce or adjust any additional liquid as needed.

For recipes like green bean casserole, you may find that you need less milk or broth because this homemade soup already has a pourable consistency.

A Little Note from My Kitchen

I love a recipe that does more than one job.

This homemade Cream of Mushroom and Onion Soup is one of those recipes.

It’s something you can make on a regular afternoon, use in tonight’s dinner, and freeze the rest for another day.

It’s simple, it’s delicious, and it makes life just a little easier.

And if there’s one thing I want you to remember as we head into the holiday season, it’s this:

You don’t have to do everything at once.

Make the soup. Freeze the soup. Thank yourself later.

Cook • Gather • Live Well.

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