Whisk together 4 tablespoons chili powder, 1/4 cup sugar, 2 tablespoons garlic, and the salt in a small bowl for dry rub.

Preheat oven to 350 degree F. Rinse and pat pork dry and place in 2 lightly oiled large baking pans. Rub pork all over with dry rub and cook in upper and lower third of oven until meat is slightly pink, about 30 minutes, depending on thickness.

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.

Preheat grill. Brush top of ribs with some of barbecue sauce and place sauce side down on a lightly oiled rack; cook over moderately high heat, turning once and basting remaining side with sauce, until browned and cooked through, about 10 minutes. Transfer ribs with tongs to a platter and let stand 10 minutes. Separate ribs by cutting between the bones with a sharp knife and serve with Confetti Coleslaw and remaining sauce on side. Makes 8 servings.