In a skillet, brown and crumble sausage; drain and set aside. In a large bowl, beat eggs; add milk, salt and mustard. Stir in bread cubes, cheese and sausage. Pour into a greased 11-in. x 7-in. baking dish. Cover and refrigerate for 8 hours or overnight. Remove from the refrigerator 30 minutes before baking. Bake, uncovered, at 350° for 40 minutes or until a knife inserted near the center comes out clean.