Spread 1 1/2 Tbsp. butter on 1 side of 4 slices of bread, and spread mustard on other side of each slice. Top mustard covered side of each bread slice with 1 slice Cheddar, followed by 1/4 each of turkey and apple slices. Spread remaining butter on 1 side of remaining 4 slices of bread and place them, butter side up, on top of apple slices.
Place sandwiches in a large skillet and cook over medium-high heat until golden, about 3 to 5 minutes per side. If skillet is too small, cook sandwiches 2 at a time, placing first batch on a plate and covering loosely with foil while cooking second batch. Serve immediately.
Maybe the apple doesn't sound right at first, but Granny Smith apples taste great with salty foods. These were great sandwiches, quite filling and very tasty! We are making them again.