Tangy, Spicy Grilled Ribs

Steps

1. 1For the Ribs: Preheat oven to 325°. Combine crushed red pepper flakes, kosher salt, light brown sugar, paprika and black pepper in a small bowl.
2. 2Cut each rack of ribs in half– this is just so you can more easily maneuver on the grill, if this spiritually horrifies you, leave the racks whole. Place ribs on large rimmed sheet pan and season on both sides with the spice rub– you should use about all of it. Wrap each rack of ribs in aluminum foil and put back on the sheet pan.
3. 3Place ribs in the oven and roast until ribs are impossibly tender, nearly falling off the bone, about 2–2.5 for St. Louis; 2.5–3 hours for baby back. Remove from the oven and let cool a bit. Slowly (and carefully) unwrap the ribs, being sure to keep all the juices in the foil before pouring them into a measuring cup or medium bowl (the juices become part of the sauce you baste with/serve alongside). You should have about ¾–1 cup of liquid, but you’ll want to skim as much fat as you can off the top.
4. 4For the Sauce and Grill: Add mustard, vinegar and light brown sugar to the bowl or measuring cup with the juices. Adjust here with more vinegar or light brown sugar as you see fit– it should be fairly tangy and not that sweet (but if you prefer a bit more of either flavor, adjust with vinegar and light brown sugar, respectively).
5. 5Assuming you’re grilling* the ribs after, heat your grill to medium high (gas, charcoal, whatever). Baste the ribs on one side with sauce and place basted-side down on the grill. Baste the other side of the ribs, close the grill then let cook until charred, 5-10 minutes depending on your grill and how strong it is. Flip the ribs and baste again. Continue flipping and basting until the ribs are charred to your liking.
6. 6*If you’re not grilling, you can baste the ribs and broil until lightly charred in all the right places, too.
7. 7DO AHEAD: Ribs can be seasoned 1 day ahead, cooked in the oven 2 days ahead.