Spray baking pan with nonstick spray, preheat oven to 375. Open can of cresent rolls, remove from can. Lay 2 of the rolls flat on floured or sprayed surface so they form a square. Pinch seams together, then roll out slightly with rolling pin until of uniform thickness and size. Lay 2 slices of lunchmeat and cheese on pastry, leaving about 1/4" from each edge. Spread with mustard to taste. Lay out two more rolls, pinch and roll with rolling pin, then carefully lift to cover lunchmeat and cheese with second piece. Overlap if possible, pinch edges until sealed. Repeat with rest of cresent rolls. Place both "pockets" on sprayed baking sheet, brush tops lightly with butter if desired, and bake for 12 minutes in preheated oven. Delicious right from the oven or reheated for lunch. NOTE: Do not use soft or processed cheese in this recipe as it turns watery and runs instead of melting into the crust.