To create a wonderful Christmas Morning Casserole, follow these straightforward instructions:

1. Preheat Oven: Start by preheating your oven to 350°F (175°C).
2. Cook Sausage: In a skillet over medium heat, cook the breakfast sausage until browned. If using a vegetarian substitute, prepare according to package instructions.
3. Whisk Eggs: In a large bowl, whisk together the eggs, milk, dried mustard, salt, and black pepper.
4. Combine Ingredients: Add the cooked sausage to the egg mixture. Stir in the cubed bread, diced bell peppers, and onions (if using). Mix well.
5. Add Cheese: Fold in one cup of shredded cheese into the mixture, leaving some for topping.
6. Transfer to Baking Dish: Grease a 9×13-inch baking dish and pour the mixture into it, spreading it out evenly.
7. Top with Cheese: Sprinkle the remaining cheese generously on top of the casserole.
8. Bake: Place in the preheated oven and bake for 45-50 minutes, or until the casserole is set and lightly golden on top.
9. Cool Slightly: Remove from the oven and let it cool for about 10 minutes before serving.
10. Garnish: Add fresh herbs as a beautiful garnish before slicing.

With these simple steps, you’ll have a beautiful and delicious Christmas Morning Casserole ready to serve!