Hands down, the only Christmas breakfast casserole recipe you need!

Preheat your oven to 350°F (175°C).
In a skillet over medium heat, cook the sausage until browned. Drain excess fat.
Grease a 9×13 inch baking dish and spread the cubed bread evenly in the bottom.
Layer the cooked sausage over the bread cubes, followed by the shredded cheese.
In a large bowl, whisk together the eggs, milk, dry mustard, salt, and pepper until well combined.
Pour the egg mixture over the layers in the baking dish, ensuring everything is evenly covered.
Sprinkle the chopped green onions and diced red bell pepper over the top, if using.
Cover the dish with foil and bake in the preheated oven for 30 minutes.
Remove the foil and bake for an additional 15-20 minutes, or until the casserole is set and the top is golden brown.
Let it cool for a few minutes before serving.
Variations & Tips
For a vegetarian version, omit the sausage and add sautéed mushrooms or spinach. You can also substitute the cheddar with Swiss or Monterey Jack cheese for a different flavor profile. If you prefer a bit of spice, consider adding a pinch of cayenne pepper or a few dashes of hot sauce to the egg mixture. This casserole can be prepared the night before and refrigerated, making it a convenient option for busy holiday mornings.