Preparation

Cook the pork

• Position a rack in the center of the oven and heat to 300°F.
• Crush the fennel, cumin, and peppercorns to a medium grind in a mortar and pestle or spice grinder. Stir in the paprika. Set aside 1 tsp. of the spice mix.
• Season the ribs well all over with kosher salt, then rub the spice mix all over. Transfer to a large roasting pan, meaty side up. Pour in the apple juice, cover tightly with foil, and cook until very tender, about 2 hours; the ribs should sag if you hold the center up with a pair of tongs. Uncover, and let cool to room temperature in the pan. (If not serving right away, wrap in foil. Refrigerate for up to 2 days, or freeze up to 1 month.)

Make the glaze

• Combine the apple juice, tomato paste, Worcestershire, sugar, mustard, oregano, garlic, and 1/2 tsp. salt in a medium saucepan. Cook, stirring occasionally, over medium-low heat for 5 minutes. Season to taste with salt.(The glaze may be made up to 3 days ahead;let cool, cover, and refrigerate.)

Finish the ribs on the grill

• Prepare a medium-high (400°F to 475°F) gas or charcoal grill fire. Brush the ribs with a thin coating of the glaze. Grill, flipping every 5 minutes or so and basting with more glaze until the glaze browns, about 15 minutes. Transfer to a cutting board, tent with foil, and let rest 5 to 10 minutes before cutting the ribs apart. Sprinkle the reserved 1 tsp. of spices over the ribs and finish with a little kosher or flaky sea salt.