Roast Lamb Recipe

Prepare and score

Remove the leg of lamb from the refrigerator 1 hour before cooking to come toward room temperature. Pat the lamb thoroughly dry with paper towels. If there is a thick fat cap, trim it to an even 1/4-1/2 inch. Use a sharp knife to make 1/2-inch deep incisions across the surface at 1-inch intervals (scoring) so marinade and garlic will penetrate.

Make the marinade

In a bowl combine chopped rosemary, chopped thyme, sliced garlic, lemon zest, lemon juice, Dijon mustard, olive oil, kosher salt and black pepper. Whisk until emulsified.

Marinate the lamb

Rub the marinade all over the lamb, forcing sliced garlic into the incisions. Make sure the undersides are coated. Place the lamb in a rimmed tray or large resealable bag and refrigerate for at least 4 hours, preferably overnight. Remove from fridge 1 hour before roasting to come to room temperature.

Preheat the oven to 230°C (450°F). While the oven heats, arrange the quartered onions, carrots, celery, smashed garlic and bay leaves in a large roasting pan to form a bed. Pour the optional red wine over the vegetables and place the marinated lamb on top, fat-side up. Pour the stock into the pan around (not over) the lamb to come about 1–1.5 cm up the sides of the vegetables; this will keep drippings from burning and produce pan juices.

Roast at high heat for 15 minutes to brown the exterior and render some fat. After 15 minutes reduce the oven temperature to 175°C (350°F). Continue roasting until the internal temperature reaches your desired doneness: 55°C (130°F) for medium-rare, 60°C (140°F) for medium, or 70°C (160°F) for well done. For a 4 kg bone-in leg, expect approximately 15–18 minutes per 500 g after the initial sear for medium-rare (total time will vary). Insert an instant-read thermometer into the thickest part of the meat, avoiding bone.

Baste and monitor: Every 20–30 minutes, spoon some pan juices over the lamb to keep the crust moist. If the pan dries out, add another 60–125 ml stock. Use foil tent during the last 15–20 minutes if the surface is browning too quickly.

Rest the lamb: When the lamb reaches desired temperature, remove it from the oven and transfer to a cutting board. Tent loosely with foil and let rest 20–25 minutes. Resting allows juices to redistribute and carries the internal temp up a few degrees.

Make pan sauce

While the lamb rests, strain the roasting pan solids into a saucepan, reserving pan juices. Skim off excess fat (or spoon fat from top). Place 250 ml of the strained pan juices in the saucepan and bring to a simmer. Whisk cornstarch with cold water to make a slurry and add a little at a time to the simmering juices until sauce thickens to your liking (about 1 tbs slurry). Taste and season with salt and pepper and add a few rosemary sprigs for aroma. If you used wine, you can reduce it before adding stock to concentrate flavor.

Carve and serve: Remove any twine from the lamb. Slice the lamb across the grain into even 1/2-inch slices. Arrange on a platter, spoon pan sauce over slices or serve on the side, and garnish with rosemary sprigs.