Melt butter in a large saute pan over medium heat. Add onions and sweat until all onions are translucent and they have reduced in volume by about half.
Stir in brown sugar, vinegar, and chipotle cinnamon rub. Cook mixture over medium low heat until onions are caramelized and there is little to no excess liquid in the pan. Remove from heat and cool. Refrigerate until needed.
Chef's Tip!
Serve as a condiment on a charcuterie board, a burger topper, add to chicken sandwiches or even on baked brie as an appetizer.
