Step 1
Mix salt black pepper white pepper cayenne and garlic powder together in a small bowl. Set spice rub aside.
Step 2
Stir Dijon mustard and vinegar together in a small bowl.
Step 3
Place ribs on a foil-lined baking sheet. Turn the ribs over so that the meat side is down. Use the tip of a small sharp knife to make some very shallow slashes every few inches through the membrane that covers the ribs. Poke the knife 3 or 4 times between each rib bone about 1/4 inch deep.
Step 4
Brush about 1/2 of the Dijon mustard mixture on top. Sprinkle with about 40% of the spice rub. Turn the rack over and brush on the rest of the mustard and vinegar mixture. Sprinkle on the rest of the rub reserving 1 or 2 teaspoons in case you want to use it to season the cooked ribs later.
Step 5
Refrigerate the ribs uncovered 4 to 12 hours before baking.
Step 6
Preheat the oven to 300 degrees F (150 degrees C). Remove ribs from the refrigerator.
Step 7
Cook in the center of the preheated oven for 1 1/2 hours. Remove from the oven and baste with the pan drippings. Continue to cook until very tender and the tip of a knife slides in very easily about 1 1/2 hours more.
Step 8
Remove from the oven baste again and let ribs rest for 15 minutes before cutting and serving.