Cook the bacon in a skillet until crispy. Remove from the pan and set aside.
Cook the jalapeno in the bacon grease until wilted. Remove from the grease and drain on a paper towel.
Pour the grease into a heat-safe container and remove any leftover in the pan with a paper towel.
Spread the pepper jelly on one slice of the bread. Then, add a slice of pepper jack cheese and cheddar cheese. Add the cooked jalapeno, spreading it evenly over the cheese. Add two slices of bacon so that they cross each other. Add the other slice of bread on top.
Melt the butter and brush half of it on the outside of the sandwich. Heat the skillet and add the sandwich, buttered side down. Cook on medium-low so the cheese has time to melt.
Use a spatula to press the sandwich. Turn when browned and brush the rest of the butter on the top of the sandwich. Cook until each side is toasted.