1. Cook the Meat and Aromatics: In a large skillet, melt the butter and sauté the chopped onion and bell pepper until softened. Add the ground breakfast sausage and cook until fully browned. Drain off any excess fat.

2. Prep the Baking Dish: Lightly grease a nine-by-thirteen inch baking dish. Set the oven temperature to three hundred fifty Fahrenheit when you are ready to bake.

3. Cube and Layer the Bread: Cut the bread into one-inch cubes. Distribute about two-thirds of the bread cubes evenly across the bottom of the prepared baking dish.

4. Add Fillings: Sprinkle the cooked sausage and vegetable mixture evenly over the bread layer. Reserve about one half cup of the shredded cheddar cheese for the topping, and sprinkle the remaining cheese over the meat. Top with the remaining one-third of the bread cubes.

5. Whisk the Custard: In a large mixing bowl, whisk together the cold eggs, whole milk, heavy cream, salt, pepper, dry mustard, and garlic powder until completely uniform.

6. Pour and Soak: Slowly and evenly pour the egg and milk mixture over the contents, ensuring every piece of bread and filling is dampened. Gently press down on the bread cubes.

7. Chill (The Critical Step): Cover the dish tightly and refrigerate for a minimum of four hours, or preferably overnight (up to twenty-four hours).

8. Bake: Remove the dish from the refrigerator and let it sit at room temperature for thirty minutes. Remove the plastic wrap, top with the reserved cheese, and bake for forty-five to fifty-five minutes.