Preheat your oven to 400 degrees. Season the racks of lamb with salt and pepper on all sides. Place the racks of lamb, fat side up, on a sheet pan. After Roast the racks of lamb in the preheated oven for about 10 minutes, flip it over and bake for another 10 minutes, then flip it again for 5 minutes for medium-rare, or until the internal temperature reaches around 130 degrees. Adjust the cooking time based on your desired level of doneness.