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 degrees F. for 45 minutes or until knife inserted midway between center and outer edge comes out clean.
Serves 6