Melt the butter over medium heat in a nonreactive saucepan. Add the onions and garlic and cook, stirring, until the onions are softened and almost translucent, about 4 minutes. Add the paprika, mustard and bay leaf, and cook, stirring, until you can smell the spices, about 30 seconds. Add the apple cider, ketchup and chipotle, bring to a simmer and cook until the sauce has thickened slightly, about 15 minutes. Add the cider vinegar and cook for an additional 5 minutes. At this point, you have a mop sauce. The liquid should be fairly tart and thin in consistency.
To make the barbecue sauce, continue cooking the sauce until thickened, for an additional 20 to 30 minutes. Taste and adjust the seasoning. Use immediately, or refrigerate in a nonreactive container for up to 2 days.