- Cut the leeks in half lengthwise and rinse in a bowl of cold water to remove any dirt or sand. Place the leeks on a hot grill or directly on a burner until they develop a nice char on the outside.
- Combine the charred leeks and all of the remaining ingredients in a blender and puree on high until smooth. Chill completely in the refrigerator before using. The marinade can be made up to 1 day in advance.
- Generously cover the racks of lamb in the lamb marinade and refrigerate for 6–12 hours.
- Let the lamb rest at room temperature for 1 hour before cooking.
- Preheat the oven to 400 degrees.
- Place the racks on a baking sheet or roasting pan and roast uncovered for 15–25 minutes or until the internal temperature of the lamb is 125–130 degrees or medium rare. You may cook the lamb longer or less depending on your preference for doneness.
- Let the lamb rest on a cutting board for 5–10 minutes.
- Slice each chop off the loin, leaving the bone in.
- Place the romesco sauce in a decorative bowl in the center of a large warmed platter.
- Arrange the lamb chops around the sauce. Garnish around the lamb with shishito peppers. Serve immediately.
- Roast the whole peppers under a broiler until charred and blackened. Place the warm peppers in a stainless steel bowl and cover with plastic wrap. When the peppers come to room temperature, carefully peel off the charred skins and set aside.
- In a small skillet or saucepan, sauté the garlic and almonds in the oil for several minutes. Do not brown.
- Combine all the ingredients in a blender. Blend and season with salt, sugar, lemon juice, and Sriracha to taste. Transfer to a small bowl.
- The sauce may be covered with plastic wrap and kept for several days in the refrigerator. Warm the sauce before serving with the lamb.
- Preheat a large cast iron skillet until it is almost smoking.
- Film the pan with grapeseed oil and add the peppers. Allow the peppers to char lightly on one side. Turn the peppers over to char the other side. Season heavily with salt and sugar and continue to roast in the pan for several minutes.