Cook egg noodles according to package directions. Drain and set aside.
In a skillet, melt butter over medium heat. Add onions and mushrooms, cook until tender.
In a large mixing bowl, combine sour cream, cream of mushroom soup, shredded cheddar cheese, cooked onions, and mushrooms. Add salt and pepper to taste.
Stir in the cooked egg noodles until well combined.
Transfer the mixture to a baking dish. Bake in the preheated oven for 30 minutes or until bubbly and golden brown on top.