Few foods are as alluring as a large rack of ribs, gently slow-cooked over charcoal and hardwood until they're lip-smackingly tender and flavorful. Cooking them from start to finish is a project for a lazy weekend, rather than a quick weeknight meal, but that doesn't mean you can't enjoy them on a busy weeknight. You can reheat the ribs quickly under a broiler or gently in the oven, with a minimum of fuss and bother.
Thaw the ribs overnight if they're frozen. Cut them into serving portions, and paint the ribs with a fresh coat of sauce, if you wish.
Arrange the racks so your ribs will be 4 to 5 inches from the broiler element, then close the oven door and preheat the broiler.
Arrange the ribs on your broiler pan with the curved side facing up, and slide them under the broiler for 2 to 4 minutes, until the sauce begins to bubble.
Turn the ribs meat-side up, and slide them back under the broiler. Heat them for 3 to 4 more minutes, for baby back ribs, or 4 to 6 minutes for larger side or spareribs. The sauce should be bubbling and caramelized, and fat should begin to ooze from the ribs.
Remove the ribs from the oven and cover them loosely with foil. Let them rest for 3 to 5 minutes before serving, so the heat can equalize throughout the ribs.
Move the ribs to the refrigerator the night before, so they're thawed by dinnertime the next day.
Preheat the oven to a moderate temperature, ideally 225 to 250 degrees Fahrenheit. Higher temperatures warm the ribs more quickly, but run the risk of making them dry.
Lay a large, doubled sheet of heavy-duty aluminum foil on your work surface. Cut the ribs into serving portions, and brush them with your favorite sauce or glaze. Arrange them in a single layer or loose stack on the foil, then fold up the sides and crimp them to make a tightly sealed packet.
Warm the ribs gently in your oven for 40 to 60 minutes, depending on their size, until they're thoroughly heated and steaming.
Unwrap the foil package and serve the ribs immediately, while they're hot and moist.