Preheat oven to 350.
Cook sausage in medium sauté pan over medium heat. Drain. Leave some drippings in pan to sauté mushrooms.
Dice mushrooms and sauté on medium-high for 5 minutes in sausage grease.
Crack 12 eggs in a large bowl and whisk until completely combined and smooth.
Add baking powder, salt and pepper. Whisk until smooth.
Next, add sour cream, and whisk until smooth.
Combine egg mixture, sautéed mushrooms, sausage and cheeses. Stir to combine completely.
Pour mixture in lined muffin tins (see note below). Fill 2/3 of the way full.
Sprinkle top with about a tablespoon of cheese.
Fill a jelly roll pan half way with hot water. Put your muffin tins in this pan to create a steam bath for your egg bites.
Bake on 350 for 23-25 minutes.