1 rack St. Louis–style pork spare ribs (about 2 pounds)
1/2 cup freshly ground black pepper
1 tablespoon ground coriander
1 tablespoon light brown sugar
1 tablespoon mustard powder
1 tablespoon smoked paprika
1/2 teaspoon cayenne pepper
1/4 cup distilled white vinegar
2 tablespoons kosher salt
1/4 cup Dijon mustard
3 tablespoons apple cider vinegar
3 tablespoons honey
2 tablespoons soy sauce
Combine black pepper, coriander, brown sugar, mustard powder, paprika, and cayenne in a small bowl. Brush ribs on both sides with distilled vinegar, sprinkle with salt, then pat all over with rub. Place on a rimmed baking sheet; chill at least 1 hour.
Place rack in lower third of oven and preheat to 325F/160C Transfer ribs to a roasting pan, fatty side up. Pour 1/2 cup water into pan and cover tightly with foil. Bake until meat is tender and falling off the bone, about 2 hours.
Remove ribs from oven and let stand, covered, 30 minutes.
Whisk Dijon mustard, cider vinegar, honey, and soy sauce in a small bowl.
Heat broiler. Remove foil from ribs and brush liberally on both sides with mustard mixture. Broil ribs until lightly charred, about 3 minutes. Slice into individual ribs.
