Add the breakfast sausage and cook it until browned, breaking it up into smaller chunks as it cooks. Leave a little grease in the pan to cook the veggies.
Add the bell peppers and onion to the same skillet you cooked the sausage and saute for 3-4 minutes until softened. Transfer the cooked vegetables to a bowl.
Add the meat and vegetable mixture to the greased pan. Top with shredded cheese.
Combine the eggs, sour cream, heavy whipping cream, and salt and pepper in a large mixing bowl. Beat with a whisk until combined. Pour the egg mixture over the top of the cooked sausage and veggies.
Bake the egg breakfast casserole in the preheated oven for 35-40+ minutes or until the edges of the casserole is set and the interior is barely jiggly.
Cut into squares. Garnish with sliced green onions. Serve with avocado slices, sour cream, hot sauce and salsa too. Enjoy!