Prepare the baking dish: Grease a 9×13-inch (23×33 cm) baking dish with butter or nonstick spray. This helps prevent sticking and encourages those nicely browned, crisp edges.
Cook the sausage: In a large skillet over medium heat, cook the breakfast sausage, breaking it into crumbles with a spatula, until browned and cooked through, 7–10 minutes. If the pan seems dry at the start, add the optional tablespoon of oil or butter. When done, drain off excess fat if there’s a lot, leaving just a light coating to keep things flavorful.
Cool the sausage slightly: Transfer the cooked sausage to a plate or bowl and let it cool for a few minutes. This prevents it from warming the eggs prematurely when you assemble the casserole.
Cube the bread: While the sausage cools, cut your bread into 1/2-inch cubes. Day-old or slightly dried bread holds up better and absorbs the custard without turning mushy. If your bread is very fresh and soft, you can lightly toast the cubes in a low oven (300°F / 150°C) for 5–10 minutes to dry them out a bit.
Whisk the egg mixture: In a large mixing bowl, whisk together the eggs, milk, salt, black pepper, garlic powder, onion powder, and smoked paprika (if using) until well combined and no large streaks of egg white remain. This mixture is your custard base and will give the casserole its tender, custardy interior.
Add cheese, peppers, and herbs: Stir in the shredded cheddar, shredded mozzarella or Monterey Jack, the diced red bell pepper, and the sliced scallions or chives. Reserve a small handful of cheese and a few pieces of bell pepper for sprinkling on top before baking, if you’d like a more decorative finish.
Combine with bread and sausage: Add the cubed bread and the slightly cooled sausage to the bowl with the egg mixture. Gently fold everything together until the bread is evenly soaked and the sausage and vegetables are well distributed. Take your time here; you want every bite to have a bit of everything.
Transfer to baking dish: Pour the mixture into the prepared baking dish, spreading it out evenly. Press down lightly with the back of a spoon or spatula to help the bread settle into the custard. Scatter the reserved cheese and bell pepper pieces over the top for color and extra browning.
Rest (optional but helpful): If you have time, cover the dish with plastic wrap or foil and refrigerate for at least 30 minutes or up to overnight. This allows the bread to fully absorb the egg mixture, resulting in a more cohesive casserole. If baking straight away, it will still work; the texture will just be slightly lighter and less custardy.
Preheat the oven: When you’re ready to bake, preheat your oven to 350°F (175°C). If the casserole has been refrigerated, remove it from the fridge while the oven heats so it can lose some of its chill.
Bake the casserole: Uncover the baking dish and place it on the middle rack of the oven. Bake for 40–50 minutes, or until the top is deeply golden brown, the cheese is bubbly, and the center is set. You can check doneness by inserting a knife or toothpick near the center; it should come out mostly clean, with no liquid egg pooling.
Garnish and rest: Remove the casserole from the oven and let it rest for 5–10 minutes. This brief rest allows the structure to set so it slices neatly. Sprinkle with additional sliced scallions or chopped chives for a fresh, green finish that contrasts nicely with the browned sausage and cheese.
Serve: Cut into squares and serve warm directly from the pan. The top should be golden and slightly crisp, with visible crumbles of sausage, bright red bell pepper, and flecks of green herbs across the surface.
Variations & Tips
This casserole is very forgiving and easy to adapt to what you have on hand. For a lighter version, you can use turkey sausage or chicken sausage instead of pork, and swap in 2% milk for whole milk. If you prefer a potato base, replace the bread with about 4 cups of thawed frozen hash browns; the texture will be a bit heartier and more reminiscent of a skillet hash. Cheese is another easy place to experiment: sharp cheddar gives a classic, robust flavor, but you can mix in pepper Jack for heat, Gruyère for a nutty note, or even a bit of feta sprinkled on top after baking for tang. Vegetables are flexible, too—try sautéed mushrooms, spinach, or onions in place of or in addition to the bell pepper. Just cook high-moisture vegetables briefly first so they don’t water down the casserole. To make it ahead, assemble the casserole the night before, cover, and refrigerate; in the morning, let it sit at room temperature for 20–30 minutes while the oven heats, then bake as directed, adding a few extra minutes if needed. If you’re cooking for a smaller household, bake the full recipe, cool completely, and refrigerate slices for up to 3 days; they reheat well in a 325°F (165°C) oven or toaster oven. You can also freeze individual portions, tightly wrapped, for up to a month—ideal for quick weekday breakfasts that still feel like a weekend treat.
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