Chop the apple and onion and sauté with the butter and brown sugar over medium heat until onion starts to caramelize. Transfer to water in a small deep pot and bring to a boil. Fry bacon until just starting to crisp. Transfer bacon with grease to boiling mixture and remove from heat. Use and immersion blender to blend ingredients fully, leaving some chunks of bacon. Transfer back to medium high heat and reduce until thick enough to spread.