My mom has always made this for us on Christmas morning, and since we only have it once a year it makes it even more good. It is so delicious, and everyone enjoys it.
Crumble sausage into a medium skillet. Cook over medium heat until evenly brown; drain.
In a medium bowl, mix together mustard powder, salt, eggs and milk. Add the sausage, bread cubes, and cheese, and stir to coat evenly. Pour into a greased 9×13 inch baking dish. Cover, and chill in the refrigerator for 8 hours, or overnight.
Preheat oven to 350 degrees F (175 degrees C).
Cover, and bake 45 to 60 minutes. Uncover, and reduce temperature to 325 degrees F (165 degrees C). Bake for an additional 30 minutes, or until set.