Add onion, garlic, one bottle of BBQ sauce, and beer, if using. Add water to cover. Mix.
Bring uncovered to boil, lower heat and simmer for at least 45 min to an hour. Remove ribs to a platter and let cool slightly. Slather generously with your remaining bottle of BBQ sauce, saving some for basting while grilling.
(At this point, you can either fire up the grill, or put the ribs away until you are ready to grill them. I often make these in the morning, and grill them in a flash for dinner.).
Preheat your charcoal or gas grill, and throw the ribs on (bone side down first) for about 10 min per side, basting with remaining BBQ sauce often. Watch so they don't burn.