Heat 1 tablespoon of butter in a large skillet over medium-high heat. Add the apples and onions, and season with salt and pepper. Cook until softened, about 5-7 minutes.
Melt remaining butter in a saucepot over medium heat. Sprinkle in flour and whisk 1 minute then whisk in stock and season with salt and pepper. Once thick enough to coat the back of a spoon, mix in cranberry sauce. Dip turkey slices into gravy.
To assemble each sammy, stack 3 to 4 slices of turkey, some apple and onion mixture, extra gravy and top with 2 slices of cheese. Place under the broiler to melt and warm through.