Crumble the sausage into a skillet. Cook over medium heat. Drain. Mix together cooked sausage, toast, cheese, mustard, salt, eggs, and milk.
Pour into a greased, 9 x 13 inch baking dish. Cover. Refrigerate overnight.
Bake, covered, at 350F.(175C.) for 45 to 60 minutes. Uncover, and reduce temperature to 325F.(165C). Bake for an additional 30 minutes, or until set.