To make the best grilled spare ribs or baby backs, bake them a day or two ahead, and make an accompanying sauce using the pan drippings. Precooking ribs tenderizes the meat, shortens cooking time and also develops a complex base flavor that comes from the melted connective tissue and liquefied marrow released as the bones break down. If you let the ribs sit in the refrigerator for a day or two after precooking them, the flavor develops even further, similarly to how the flavor of braises improve when you let them sit overnight.
Take the ribs out of the refrigerator about 1 hour before you plan to cook them, and let them sit at room temperature.
Preheat the oven to 350 degrees Fahrenheit.
Check the underside of the ribs for a thin, opaque connective membrane covering the bones. Pry up a corner of it with a paring knife and pull it off.
Season the ribs on both sides with kosher salt and your favorite spice rub or choice of spices.
Wrap each rack of ribs in two layers of aluminum foil.
Place the ribs in a roasting pan and then in the oven. Bake until tender—about 2 hours for baby back ribs or 3 hours for spare ribs.
Take the ribs out of the oven and let them cool to room temperature.
Unwrap the ribs over the roasting pan to collect the juices, and transfer the juices to a bowl or container to reserve for making a sauce.
Wrap the ribs in aluminum foil and let them sit in the refrigerator for at least 30 minutes and up to 3 days.
Mix the reserved rib juices with enough water or stock to measure about 1 cup. Add your favorite barbecue sauce to make a basting sauce for the ribs.
Finish the ribs by cooking them for about 7 to 10 minutes on a grill heated to medium. Baste the ribs frequently.