
In a small bowl, stir together the maple syrup and bourbon. Heat a cast iron skillet over medium heat. Cook the 4 bacon pieces on once side, using a cast iron bacon press to keep the bacon flat. Cook for about 4 minutes and flip the bacon. Brush the bacon with the maple bourbon sauce and cook, with a cast iron press, for 2 more minutes or until it is crispy - to your liking. Remove the bacon to a paper towel-lined plate to drain. Set aside to drain and cool.
In the same skillet with the bacon drippings, return to medium heat and melt 1 Tablespoon of the butter. Put 1 slice of the bread in the pan. Add a slice of Muenster cheese, 2 bacon slices, 4 apple slices, and then the last slice of Muenster cheese. Spread the last Tablespoon of butter on the remaining piece of bread and place on top of the sandwich, butter side up. Use a spatula to press down on the sandwich, cooking until that pan side is lightly browned. Them flip the sandwich and cook the other side until that is lightly browned and the cheese is melted. Serve immediately.