Preheat oven to 350 degrees.
Cook bacon to your liking in an oven safe pan. While bacon cooks: Slice cheese and make spicy brown mayo by whisking together mayo and spicy brown mustard. When bacon is done cooking, remove form pan and use a paper towel to wipe the pan clean.
Heat the pan med/high heat. Spread a generous amount of spicy brown mayo one side of each bread slice, reserving the rest for dipping. When pan is hot, add add 2 Tablespoons butter to the pan, spreading it out to evenly coat the pan. Place bread in the pan (mayo side up)
Add cheese to each piece of bread, then add three slices of bacon to two pieces of bread (the other two pieces of bread will top the sandwich). When bread is toasted to a nice golden color place pan into the oven until cheese is bubbly and melted.
While cheese melts, slice apples.
Remove pan from oven, add apple slices and put the sandwiches together. Serve!