How to Make It
Let the lamb stand at room temperature for 1 hour. Preheat the oven to 400°. Using the back of a knife, smash the garlic to a paste. Scrape into a small bowl and whisk in the rosemary and olive oil. Season the lamb generously with salt and pepper and rub the paste all over the lamb. Transfer to a shallow roasting pan.
Roast the lamb for about 1 hour and 15 minutes, until an instant-read thermometer inserted in the thickest part registers 130°. Transfer the lamb to a carving board and let rest for 15 minutes. Carve the lamb and serve.