In a large mixing bowl add the cream of mushroom soup, 1 cup of sour cream, 28-ounce can of drained green beans, and 1/3 cup of the onions.
Mix all of these ingredients together until evenly incorporated.
Pour into an 8×8 baking dish, and top with remaining onions.
Cover and bake at 350˚ for 30 minutes.
During the last 5 minutes, remove the foil from the baking dish and brown the top of the casserole.
Notes
You can make this recipe ahead of time! Before you add the remaining onions to the top of the casserole, wrap the dish in plastic wrap. Keep in the fridge for up to 3 days. Bake accordingly.