Begin by preheating the oven to 350°F and oiling an oven-safe baking dish that’s about 9x13” or holds at least 3 quarts.
Fry the breakfast sausage in a large skillet over medium heat. Use a wooden spoon or spatula to break it up into small pieces as it cooks.Continue cooking until the sausage is completely cooked, with no pink left. Place a colander over a bowl and drain the extra fat off of the sausage. Allow it to harden, then throw it out.Do not pour the grease down the sink, as it will harden and clog the drain.
Wash and prepare the vegetables. If you are planning to add any cooked veggies to your casserole (see the recipe notes), cook them and set aside.
In a large mixing bowl, crack the eggs and beat them with the whipping cream until smooth.
Stir in the salt and pepper.
Mix in the vegetables, breakfast sausage, and 1 cup of the shredded cheese.
Pour the mixture into the prepared baking dish.
Sprinkle the remaining cheese over the top of the casserole.
Bake the breakfast casserole for 35-40 minutes, or until it is evenly puffed, and the eggs are set when you gently press on the center of the casserole. If they aren’t cooked through, the center will have a lot of give and you’ll see wet egg seeping through the top of the casserole.
Remove the baked casserole from the oven and allow it to cool slightly. Serve it warm, with sour cream if desired.