2 half racks of American lamb (1 to 1-1/4 pounds each)
2 teaspoons vegetable oil
2 cups fresh (soft) bread crumbs
3 tablespoons finely grated parmesan cheese
4 cloves minced garlic
2/3 cup chopped fresh sage leaves
1/4 cup olive oil
2 tablespoons Dijon mustard
aged balsamic vinegar, to taste
Preheat the oven to 475 degrees. Season the racks generously with salt and pepper. Place a large cast-iron skillet over high heat. When very hot, add the oil and sear one of the lamb racks all over until it is very brown, about 2 minutes per side. Transfer to a roasting pan fitted with a wire rack, laying it with the round-side (the side with the fat) up. Repeat with the remaining rack of lamb. Cover with foil and set aside.
Place the remaining ingredients, except for the balsamic vinegar, in the bowl of a food processor. Add 1/2 teaspoon salt and pepper and process until it forms a paste. Press the paste onto the rounded side of the racks. Roast until desired doneness, about 15 minutes for medium rare. Allow to rest for 5 minutes, covered, before carving and serving drizzled with balsamic vinegar.