Melt butter in a large skillet over low heat; add onion and garlic, and sauté until tender.

Add remaining ingredients, except ribs, and bring to a boil. Reduce heat, and simmer for 20 minutes, stirring occasionally.

Build a banked fire bed in a covered grill. Place ribs on grill over indirect heat; close grill hood. Roast for 1 1/2 hours and then begin basting with sauce every ten minutes, for 30 more minutes. Remove ribs from grill and serve, cutting into serving-size portions. If desired, serve any remaining sauce on the side, bringing it to a boil and boiling gently for 5 minutes.