Step 1: Preheat the Oven
Preheat your oven to 200°C (180°C fan) or 400°F.
Step 2: Prepare the Lamb
- Pat the lamb dry with paper towels.
- Using a sharp knife, make small incisions all over the lamb. Insert a slice of garlic and a small piece of rosemary into each incision.
- Rub the lamb with olive oil, salt, and pepper.
Step 3: Prepare the Roasting Pan
- Scatter the onion slices and chopped carrots in the bottom of the roasting pan.
- Place the lamb on a rack over the vegetables.
Step 4: Roast the Lamb
- Roast the lamb for 20 minutes to sear and brown the exterior.
- Reduce the oven temperature to 160°C (140°C fan) or 320°F and roast for another 2-2.5 hours, or until the internal temperature reaches 60°C (140°F) for medium-rare or 70°C (160°F) for well-done.
- Baste the lamb every 30 minutes with the pan juices.
Step 5: Rest the Lamb
Remove the lamb from the oven and cover with foil. Let it rest for 15-20 minutes before carving to retain its juices.
Step 6: Make the Gravy
- Place the roasting pan with the vegetables and juices on the stove over medium heat.
- Sprinkle the flour into the pan and stir to combine. Cook for 1-2 minutes.
- Gradually add the stock and red wine or vinegar, stirring constantly to avoid lumps.
- Simmer until the gravy thickens. Strain if desired.
Step 7: Serve
Carve the lamb and serve with the gravy on the side. Pair with your favorite sides for a complete meal.