Step 1: Prepare the Sausage

1. Heat a large skillet over medium-high heat.
2. Add the breakfast sausage, breaking it up with a wooden spoon as it cooks. Cook for 6–8 minutes, or until the sausage is browned and no longer pink.
3. Transfer the cooked sausage to a paper towel-lined plate to drain excess grease.

Step 2: Prepare the Bread and Cheese Layers

1. Cut the bread into 1-inch cubes. Use day-old bread if possible, as it absorbs the egg mixture better without becoming soggy.
2. Grease a 9×13-inch baking dish with cooking spray or butter.
3. Arrange the bread cubes evenly in the prepared baking dish.
4. Sprinkle the cooked sausage over the bread cubes.
5. Layer the shredded cheddar, mozzarella, and Parmesan cheese on top of the sausage.

Step 3: Make the Egg Mixture

1. In a large mixing bowl, whisk together the eggs, whole milk, garlic powder, onion powder, salt, and black pepper.
2. Pour the egg mixture evenly over the bread, sausage, and cheese layers. Use a spatula to press the bread cubes down gently, ensuring they soak up the liquid.

Step 4: Add Optional Ingredients

If you’re adding vegetables such as bell peppers, onions, spinach, or mushrooms, sprinkle them evenly over the top of the casserole before baking.

Step 5: Bake the Casserole

1. Preheat your oven to 350°F (175°C).
2. Cover the baking dish with aluminum foil and bake for 30 minutes.
3. Remove the foil and bake for an additional 10–15 minutes, or until the top is golden brown, the cheese is bubbly, and the eggs are fully set.
4. To check doneness, insert a knife into the center of the casserole. If it comes out clean, the casserole is ready.

Step 6: Rest and Serve

1. Allow the casserole to rest for 5–10 minutes before slicing.
2. Garnish with fresh parsley or chives for a pop of color. Serve warm and enjoy!