Step 1: Preheat the Oven

1. Preheat your oven to 375°F (190°C).
2. Lightly grease a 9×13-inch casserole dish with cooking spray or butter.

Step 2: Prepare the Biscuit Layer

1. Open the can of biscuits and cut each biscuit into quarters.
2. Arrange the biscuit pieces evenly across the bottom of the greased casserole dish.

Step 3: Cook the Sausage (if needed)

1. If using raw sausage, cook it in a skillet over medium heat until fully browned, breaking it into crumbles. Drain any excess grease.
2. Spread the precooked or freshly cooked sausage evenly over the biscuit layer.

Step 4: Add the Cheese

1. Sprinkle the shredded mozzarella and cheddar cheese evenly over the sausage layer.

Step 5: Prepare the Egg Mixture

1. In a mixing bowl, whisk together the beaten eggs, milk, salt, and pepper.
2. Stir in any optional sautéed veggies if desired (e.g., spinach, mushrooms, red peppers).

Step 6: Combine the Layers

1. Slowly pour the egg mixture evenly over the biscuit, sausage, and cheese layers.
2. Press down gently with a spatula to ensure everything is coated.

Step 7: Bake the Casserole

1. Bake the casserole in the preheated oven for 25–30 minutes, or until the eggs are set and the top is golden brown.
2. Check doneness by inserting a toothpick or knife into the center; it should come out clean.

Step 8: Cool and Serve

1. Allow the casserole to rest for 5 minutes to set before slicing into squares.
2. Serve warm and add your favorite toppings like green onions, salsa, sour cream, or hot sauce.