Preheat your oven to 350°F.
Using a knife, cut the white bread into 1/2-inch cubes and set them aside.
In a large skillet, brown the pork sausage until cooked through, then drain any excess fat.
In a mixing bowl, whisk the eggs, milk, salt, and ground mustard.
Add the browned sausage, bread cubes, and shredded Cheddar cheese to the mixing bowl and stir until everything is well combined.
Lightly grease a 9x13 inch baking dish with cooking spray.
Pour the mixture into the baking dish and spread it out evenly.
Cover the baking dish with plastic wrap and refrigerate for at least 8 hours or overnight to allow the flavors to meld.