In a saucepan over medium heat, melt the butter and sweat the onions and garlic.
Sweat: Sweating is the process of releasing flavors with moisture and low temperatures. Fat, in this case, is used just to hold the non-volatile flavors as they are released from the onion. No browning takes place. The pan is covered so the lid traps steam, which condenses and drips back on to the onions.
When onions and garlic are translucent, stir in the chipotle chile pepper and chili powder. When the chili powder just begins to release their aroma, stir and add the blackberries, molasses, honey, cider vinegar, balsamic vinegar, red wine vinegar, Worcestershire sauce, soy sauce, and water. Let simmer for 30 minutes. Lightly season with salt and pepper and remove from stove.
NOTE: Blackberry Barbecue Sauce can be stored in air tight container in refrigerator for up to 5 days.
Yields 3 cups sauce.
Blackberry Barbecue Sauce Recipe: https://whatscookingamerica.net/doc-lawrence/celebratingredwhiteblue.htm