Brown the breakfast sausage in a large skillet over medium heat, breaking it into crumbles, then drain and set aside.
Grease a 9x13-inch baking dish and layer the bread cubes evenly on the bottom.
Sprinkle the cooked sausage and shredded cheese over the bread cubes.
In a large bowl, whisk together eggs, milk, dried mustard, salt, and pepper until well combined.
Pour the egg mixture evenly over the bread, sausage, and cheese, pressing down gently to ensure all bread is moistened.
Cover with plastic wrap and refrigerate overnight or for at least 8 hours.
Remove from refrigerator 20 minutes before baking and preheat oven to 350°F.
Bake uncovered for 45 minutes or until the top is golden brown and the center is set.