Cut strips of bacon crosswise into 1/2-inch pieces. Cook 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 refrigerate overnight.
Remove from refrigerator and let stand at room temperature for 15 minutes.
Bake, uncovered, at 325° F for 45 minutes or until knife inserted midway between center and outer edge comes out clean.Makes 6