For the cure: Combine the salt and pepper in a bowl. Generously cover the ribs with the cure. Place the ribs, uncovered, on a rack set in a baking pan or a tray. Marinate for 24 hours in the refrigerator. Rinse the ribs well under cold water, and pat dry thoroughly.
For the dry rub: Toast the peppercorns and fennel seeds in a dry saute pan until fragrant, 2 to 3 minutes. Using a mortar and pestle or spice grinder, grind the toasted spices. Combine the ground peppercorns and fennel seeds with the paprika, dried sage, dried thyme, granulated garlic, onion powder, sugar and bay leaf powder in a bowl, stirring to combine thoroughly.
Preheat the oven to 275 degrees F. Line a baking sheet with foil and scatter the onions on the foil. Sprinkle the dry rub liberally over both sides of the ribs and place them, bone-side down, on top of the onions to prevent sticking. Add the vinegar to the pan and sprinkle the fresh thyme leaves over the ribs. Top with another piece of foil and crimp the edges together with the bottom piece of foil to create a large foil pouch. Roast until the ribs are tender and the meat has shrunk back from the bone, approximately 1 1/2 hours.
Pour the pan juices through a strainer to remove the onions. Skim the fat and simmer the juices with the chicken stock in a saucepan over high heat until reduced by half.
Cut the lamb racks into double rib portions, drizzle lightly with olive oil and sprinkle with a little salt. Crisp the exterior of the ribs on a hot grill or under a broiler for 5 minutes (meat-side only), basting occasionally with the reduced pan juices. Serve drizzled with the apricot mint chimichurri.
Apricot Mint Chimichurri:
Yield: About 2 cups
Place the apricots and 1 teaspoon honey in a heat-proof bowl and cover with boiling water. Soak the apricots for 10 minutes to plump. Remove the apricots from the hot water and roughly chop.
In a food processor, combine the mint, parsley, cilantro, vinegar, lemon zest and juice, garlic, adobo sauce, cumin, paprika, salt, black pepper, red pepper, remaining tablespoon honey and olive oil and pulse until finely chopped. Add the rehydrated apricots and pulse until the consistency resembles a thick chunky sauce. Cover and store in the refrigerator to allow flavors to come together and serve with grilled meats.