How to Make It
In a medium saucepan, bring 2 bottles of the root beer to a boil with the fish sauce, garlic, cracked black peppercorns and shallots. Remove from the heat, cover and let steep for 25 minutes. Transfer the mixture to a large roasting pan and add the ice. Add the rib racks, cover and refrigerate overnight.
Preheat the oven to 325°. Remove the ribs from the marinade and scrape off most of the solids. Transfer the ribs to a large rimmed baking sheet. Cover with foil and bake for about 2 hours, until the meat is very tender but not falling off the bones.
Meanwhile, in a medium saucepan, combine the remaining 2 bottles of root beer with the vanilla bean and seeds and long pepper and boil over moderately high heat until reduced to 2/3 cup, about 25 minutes. Add the lime juice and simmer for 2 minutes. Discard the vanilla bean.
Light a grill. Grill the ribs over high heat until richly browned, about 4 minutes per side. Transfer the racks to a carving board and cut in between the ribs. Serve the ribs with lime wedges, passing the root beer sauce at the table.
Long pepper, a fragrant relative of black pepper from Indonesia, can be found at specialty food stores and online at salt traders.com.