Step 1

Blot any moisture from the surface of the lamb with paper towels and lightly score a crisscross pattern on the fatty side with a sharp knife.

Step 2

Mix the olive oil with the grated garlic, diced rosemary, salt, and pepper. Brush it all over the lamb and leave uncovered in the fridge for at least 4 hours.

Step 3

Remove the lamb leg from the fridge and let it come to room temperature (at least 30 minutes).

Step 4

Preheat the oven to 190°C/375°F (no fan).

Step 5

Place the lamb fat side down on a roasting tray with a rack and roast for 30 minutes.

Step 6

Turn the lamb over so it is fat side up, and roast for another 15 minutes.

Step 7

Turn the oven down to 175°C/345°F and roast for a further 30-45 minutes or until the lamb leg reaches your desired internal temperature (see notes below).

Step 8

Rest the lamb for 15-20 minutes before carving and serving.

Step 9

In the roasting pan, slowly whisk two to three teaspoons of flour into the lamb drippings until you have a smooth, thick paste (a roux).

Step 10

Heat lamb or vegetable stock in a pan to a gentle simmer and then whisk a ladleful into the roux to loosen the paste.

Step 11

Add the loosened roux into the saucepan and cook at a gentle simmer for 10 minutes until it thickens. Season to taste and sieve into a serving jug.