Season the meaty side of each rack with 3/4 teaspoon of the Essence.
Melt the butter in a medium skillet over medium-high heat. Add the onions, celery, shallots, 1/4 teaspoon of the salt, and the pepper and cook, stirring often, until the vegetables begin to soften, about 1 minute. Add the garlic and stir until fragrant, about 30 seconds. Add the apricots, raisins, and prunes and cook until softened, 2 to 3 minutes. Add the port wine and cook until almost all the liquid has evaporated, about 5 minutes. Stir in the walnuts and mint.
Remove from the heat and let cool for 10 minutes. (If desired, the stuffing can be made 1 day ahead and refrigerated, tightly covered.)
Preheat the oven to 400?F.
One rack at a time, with a thin sharp knife, cut into the center of the lamb loin from one end, going into the meat as deep as you can. Turn the lamb and cut into the center from the other end, to make one long hole through the meat. Insert a long-handled wooden spoon into the hole and push the handle through to the other side. Gently work the spoon handle to enlarge the hole to 1/2 to 3/4 inch in diameter.
With your fingers, work about one-fourth of the fruit stuffing into the center of the meat so that the hole is filled with stuffing. Repeat with the remaining racks and stuffing.
Heat a heavy nonstick skillet over medium-high heat. In batches, add the racks to the skillet and sear, turning occasionally, until browned on all sides, about 7 minutes.
Meanwhile combine the bread crumbs, olive oil, the remaining 1 tablespoon essence, and the remaining 1/2 teaspoon salt in a shallow bowl.
Spread 2 tablespoons of the mustard on each rack, then dredge in the seasoned bread crumbs, coating evenly. Place the lamb on the meaty side in a roasting pan. Cover the bones with aluminum foil to prevent them from burning. Roast for 20 to 25 minutes, until an instant-read thermometer inserted in the thickest part of the racks reads 125?F, for medium-rare.
Let stand for 5 minutes before slicing into chops.
Yield: 4 servings