Meanwhile, heat 3 tablespoons oil in a large saucepan over moderately high heat until hot but not smoking and cook onion, stirring, until softened, about 8 minutes. Add remaining 6 tablespoons chili powder and 4 tablespoons garlic; cook, stirring, 1 minute. Stir in ketchup, coffee, vinegar
, and remaining 1/4 cup sugar; simmer, stirring occasionally, until reduced to 4 cups, about 40 minutes. Remove pan from heat, transfer 2 cups sauce to a bowl for basting and place remaining sauce in a small bowl for serving on side.