Prepare Casserole Base
Combine eggs, sour cream, milk, cheese, salt, and pepper. Mix until combined.
Cook Sausage and Vegetables
Cook sausage until browned, breaking into small pieces. Drain most grease.
Sauté bell peppers and onion for 2-3 minutes.
Add cooked sausage, bell peppers, and onion to the egg mixture. Stir to combine.
Bake Casserole
Pour mixture into a pan.
Bake 35-50 minutes, until edges are set and center is jiggly.
