Score the fat of the lamb racks with a knife and season with salt and pepper.

In a small food processor or blender, combine the garlic, mint, thyme, and rosemary. Pulse several times. Add the oil and process until smooth. Rub all over the lamb, place the lamb in a large food storage bag, and let sit at room temperature for 1½ hours or until the lamb is room temperature.

Preheat the oven to 450°F. Heat a large cast iron skillet over high heat. Sear the lamb on all sides, about 5 minutes per rack. Place the racks back in the skillet, fat side up, and roast for 12-18 minutes, depending on desired doneness. Internal temperature is 115-120°F for rare, 125°F for medium-rare, 130°F for medium, 145°F for medium-well, 150°F for well done.

Let the lamb racks rest for 15 minutes before serving