In a food processor, combine the garlic, rosemary and olive oil and process until the garlic is finely chopped. Season the lamb racks with salt and pepper and rub the garlic-rosemary oil all over them. Set the racks fat side up on a large rimmed baking sheet and let stand for 1 hour.
Preheat the oven to 450°. Roast the lamb in the upper third of the oven for 15 minutes. Turn the racks and roast for 10 minutes longer for medium-rare meat. Transfer the racks to a carving board, stand them upright and let rest for 10 minutes.
Carve the racks in between the rib bones and transfer to plates. Serve right away.
Recipe by Lone Star Lamb at https://lonestarlamb.com/2018/03/01/garlic-crusted-roast-rack-of-lamb/