Cut rack into individual ribs and place onto foil-covered, oiled baking sheet. Sprinkle with salt and pepper. Bake at 400°F for 15 minutes.
Meanwhile, mix onion, garlic, sugar, vinegar and barbecue sauce in a sauce pan and simmer over medium heat until bubbling. Remove sauce from heat and set aside.
Remove ribs from the oven, coat each rib in sauce and return to the oven. Continue to bake ribs for four hours at a reduced temperature of 300°F, re-coating ribs with sauce every hour.
Serve with sides of barbecue baked beans and cole slaw.