Chop and brown sausage in a 10-inch skillet. Drain as much grease as possible. While meat is cooling, arrange bread slices in the bottom of a 9 x 13 x 2-inch cake pan to form a crust base. Crumble sausage over bread. In a medium bowl, mix eggs, milk and mustard and pour carefully over sausage and bread. Sprinkle cheese over mixture. Cover and refrigerate overnight. Uncover and bake in 350° oven for 1 hour.