1-Getting started with this roast lamb: First, take the lamb out of the fridge at least 1 hour before roasting to let it reach room temperature, which helps it cook evenly. Next, preheat your oven to 240°C (475°F), or 220°C (425°F) if you’re using a fan oven, and position the rack in the middle for optimal heat flow.

2-Mix up the rub: Combine the finely chopped rosemary, minced garlic, and olive oil in a small bowl. Place the lamb in a roasting pan and rub it all over with this mixture, making sure it’s evenly coated for maximum flavor. Season it with the salt and black pepper, then add the two halved garlic heads and rosemary sprigs cut side up under the lamb in the pan.

3-Roast at the high temperature: Roast at the high temperature for 20 minutes to get that nice color and crust. Then, lower the heat to 200°C (400°F), or 180°C (350°F) for fan ovens, and keep roasting for about 1 hour until the internal temperature hits 53°C (127°F) for medium rare check around 45 minutes to see how it’s going. Once done, take the lamb out, cover it loosely with foil, and let it rest for 20 minutes to 1 hour; this lets the temperature rise to about 62°C (144°F) for that perfect medium rare.

4-Making the Gravy: While the lamb rests, turn to the roasting pan for gravy. Remove the rosemary sprigs, place the pan on the stove over medium heat, and warm the drippings. Stir in the flour and cook for 1 minute to avoid lumps, then slowly add the beef broth while stirring to blend everything smoothly.

Use a potato masher to press the roasted garlic halves and release their flavor into the mix. Let it simmer until it thickens a bit, taste it, and add salt and pepper if needed. Strain out the solids before serving for a smooth finish. Finally, serve the lamb with this gravy and sides like peas, buttered steamed carrots, and crispy roast potatoes for a complete meal.