Gather all ingredients before starting recipe.
Pre heat oven to 350°F
Slightly thaw 2 lbs frozen hash brown potatoes.
Mix 2 cups sour cream, 2 cans (11 oz) cream of mushroom soup, 1/4 cup melted butter, 1 small grated onion, and 2 cups grated cheddar cheese and blend with the slightly thawed hash brown potatoes.
Pour mixture into a buttered casserole dish and sprinkle 2 tbsp grated parmesan cheese (optional) or more parmesan cheese on top.
Bake in a pre-heated oven for 60 minutes.
Allow to cool slightly before serving.
