For bacon jam: Cut bacon into half-inch pieces. Place in pan over medium heat until cooked but still chewy, stir frequently, about 10 minutes.
Remove bacon from pan using a slotted spoon. Remove 2 tablespoons of rendered bacon fat. Place in small bowl and set aside. Discard remaining bacon grease from pan.
Add onions to pan and cook for 10 minutes. Reduce heat to low, add sugar and stir. Continue cooking until onions have caramelized, about 10 minutes.
Add coffee and reserved bacon fat to pan. Increase heat to medium and stir every 5 minutes until mixture thickens and becomes jam-like, about 15-30 minutes. Remove from heat and add balsamic vinegar. Stir to combine.
Store in refrigerator for up to one week.
For sandwich assembly: Heat grill press.
Cut roll in half and place butterkäse slices on one half; roll should be fully covered by cheese. Spread a thick layer of bacon jam on top of the butterkäse and then place sharp cheddar slices on top of the bacon jam. Next, layer chicken on top of the sharp cheddar and add a layer of kimchi. Place muenster slices on top of the layer of kimchi and place the remaining half of the roll on top.
Place sandwich on grill and lower lid; apply gentle pressure. Cook until cheese melts, about 7 minutes.
If you do not have a grill press, the sandwich can be made with a skillet. Add 1 tablespoon of olive oil to skillet and heat to medium. Place sandwich in pan and cover until cheese melts.
Remove from grill (or skillet) and place on plate. Cut in half and enjoy.
For Bacon Jam:
- 1 1/4 pounds thick cut bacon
- 2 large sweet onions, quartered and sliced
- 1/2 cup brown sugar
- 1 cup strong coffee, brewed
- 2 tablespoons balsamic vinegar