How to Make It
Preheat the oven to 450°. In a medium saucepan, bring the chicken stock to a simmer over moderate heat. Stir in the miso until dissolved. Add the blue cheese and stir until dissolved. Add the soy sauce and mirin and simmer for 1 minute, stirring constantly. Strain the sauce into a clean saucepan.
Season the lamb racks with salt and white pepper. In a large ovenproof skillet, heat 2 tablespoons of the oil until almost smoking. Set the lamb racks in the skillet, fat side down, and sear over high heat until nicely browned, about 5 minutes. Turn the racks over and brown the bottoms, about 3 minutes. Transfer the skillet to the oven and roast the lamb for about 25 minutes for medium rare, or until an instant-read thermometer inserted in the thickest part of the meat registers 125° to 130°. Transfer the racks to a cutting board, cover loosely with foil and let rest for 10 minutes.
Meanwhile, in a medium skillet, heat the remaining 1 tablespoon of oil. Add the red pepper and cook over moderately high heat until barely tender, about 2 minutes. Add the arugula and stir until just wilted. Season with salt and white pepper.
Reheat the sauce and season with salt and white pepper. Transfer the arugula mixture to 4 large plates. Carve the racks into individual chops and arrange 4 on each plate. Spoon about 1/4 cup of the miso-blue cheese sauce over and around the meat. Sprinkle with the chives and black sesame seeds and serve at once.