Instructions

1. Melt butter in medium saucepan over medium heat. Add onion and cook until softened. Add garlic and cook for about 30 seconds until fragrant.
2. Add ketchup, molasses, brown sugar, vinegar, mustard, chili powder, black pepper, and cayenne pepper and stir to combine. Bring to a boil, then reduce heat to low and simmer until slightly thickened, about 30 minutes, stirring frequently.
3. Transfer sauce to the jar of a blender and blend until smooth. Let cool to room temperature, trasfer to a jar and store in refrigerator for up to a month.