Start by preheating your oven to 350°F (175°C). While it’s warming up, take the leg of lamb out of the refrigerator. This allows the meat to reach room temperature, ensuring even cooking. Pat the lamb dry with paper towels, which helps develop a beautiful crust.

Drizzle the olive oil over the lamb, making sure to coat it evenly. Rub the balsamic vinegar into the meat, enhancing the flavor. Generously season with sea salt and freshly cracked black pepper. Let’s not skimp on seasoning; it’s key to a flavorful dish.

Take your garlic bulbs and rosemary sprigs, pressing them gently into the meat. The garlic will roast beautifully, becoming soft and sweet, while the rosemary infuses the lamb with its fragrant aroma.

In a roasting pan, place the quartered onion around the lamb. You can also add other vegetables like carrots and potatoes if you’d like. They will soak up the delicious juices from the lamb.

Pour the beef broth into the pan, ensuring it doesn’t touch the lamb directly. This broth will keep the meat moist while roasting and serve as the base for your gravy.

Cover the pan with aluminum foil, making sure it’s secure to trap in moisture. Place it in the preheated oven for about 2 hours. If you prefer medium-rare, aim for an internal temperature of 145°F (62°C). Use a meat thermometer to ensure accuracy.

After the initial roasting, uncover the lamb for the last 30 minutes. This step allows the surface to caramelize, resulting in a hearty, golden crust. Baste the lamb with the pan juices once or twice during this time.

Once the lamb reaches your desired temperature, it’s essential to let it rest for about 15 minutes before carving. Resting allows the juices to redistribute throughout the meat, enhancing the flavor and tenderness.

While the lamb rests, use the drippings in the pan to create your gravy. Pour the liquid into a saucepan and bring it to a simmer. In a separate bowl, mix the flour with water until smooth. Gradually whisk this mixture into the simmering liquid until thickened. Season with salt and pepper to taste.

Now comes the exciting part: carving the lamb! Use a sharp knife to slice the meat against the grain. Serve it on a platter, drizzled with gravy, and accompanied by your favorite sides.