Cut strips of bacon crosswise into 1/2-inch pieces. Cook bacon in skillet over medium heat until crisp; blot with paper towels. Discard accumulated bacon fat. Remove crusts from bread, and reserve for another use. Cut bread slices into cubes; set aside. In a large bowl, beat eggs, stir in milk, cheese and mustard. Gently stir bacon and bread cubes into egg mixture; spoon into buttered 8-inch square baking dish. Cover tightly and refrigerator overnight. Remove from refrigerator and let stand at room temperature for 15 minutes. Bake, uncovered, at 325° for 45 minutes or until knife inserted midway between center and outer edge comes out clean.