Making this breakfast casserole is incredibly easy, even for beginner cooks. The beauty lies in its make-ahead nature, allowing you to prepare most of it the day before and simply bake it in the morning. Follow these simple steps for breakfast casserole success:

1. Prepare the Sausage and Vegetables: Begin by cooking your breakfast sausage in a skillet over medium heat. Break it up into crumbles as it cooks. Once fully cooked, drain off any excess grease. If you’re using onions and bell peppers (and we highly recommend it!), sauté them in the same skillet after removing the sausage. Cook them until they are softened and slightly translucent, about 5-7 minutes. This step enhances their flavor and texture in the final casserole. Set the sausage and vegetables aside to cool slightly.
2. Prepare the Bread: Cube your bread into approximately 1-inch pieces. If you’re using fresh bread, you can lightly toast the cubes in the oven for a few minutes to dry them out slightly. This helps them absorb the egg mixture without becoming too soggy. Day-old bread is perfect as it already has a slightly drier texture.
3. Whisk the Egg Mixture: In a large bowl, whisk together the eggs and milk until well combined. Season generously with salt and pepper. Don’t be shy with the seasoning – it’s crucial for flavorful casserole. Taste the mixture and adjust seasoning as needed. If you’re adding any optional spices like garlic powder or paprika, whisk them in at this stage.
4. Assemble the Casserole: Now it’s time to layer everything together. In a greased 9×13 inch baking dish, arrange the cubed bread in an even layer at the bottom. Distribute the cooked and crumbled sausage evenly over the bread. If you sautéed vegetables, scatter them over the sausage layer as well. Finally, sprinkle the shredded cheese generously over the top.
5. Pour the Egg Mixture: Gently pour the egg and milk mixture evenly over the entire casserole, ensuring that it soaks into the bread. Use a spoon or spatula to lightly press down on the bread to help it submerge in the liquid. This ensures that every piece of bread is coated and becomes deliciously custardy when baked.
6. Chill (Make-Ahead Option): This is where the “make-ahead” magic happens! Cover the assembled casserole tightly with plastic wrap or aluminum foil and refrigerate for at least 2 hours, or ideally overnight. Chilling allows the bread to fully absorb the egg mixture, resulting in a more flavorful and cohesive casserole. If you are baking it immediately, you can skip the chilling step, but the texture and flavor will be even better if you chill it first.
7. Bake the Casserole: When you’re ready to bake, preheat your oven to 350°F (175°C). Remove the casserole from the refrigerator and let it sit at room temperature for about 15-20 minutes while the oven preheats. This helps it bake more evenly. Bake uncovered for 45-60 minutes, or until the casserole is golden brown and set, and a knife inserted into the center comes out clean. The baking time may vary slightly depending on your oven and the depth of your baking dish.
8. Rest and Serve: Once baked, remove the casserole from the oven and let it rest for 5-10 minutes before serving. This allows the casserole to set further and makes it easier to slice and serve. Resting also helps to prevent it from being too runny. Slice into squares and serve hot.