Preheat the oven to 180°C (350°F).

Cut the potatoes and carrots into chunks about 2 inches in size so they cook evenly. No need to peel.

Peel the onions and cut them into large chunks.

Spread the potatoes, carrots and onions across the base of a deep roasting tin. Drizzle with 1 tablespoon of olive oil and sprinkle lightly with salt.

Place the leg of lamb on top of the vegetables, skin side up.

Using a sharp knife, pierce the lamb 20–30 times across the surface.

Rub the lamb with the remaining 1 tablespoon olive oil and sprinkle with about 1 teaspoon salt.

Slice 4 cloves of garlic and insert a slice of garlic and a small sprig of rosemary into each of the holes in the lamb.

Scatter the remaining garlic cloves and rosemary over the vegetables. There is no need to peel the extra garlic cloves.

Pour the stock over the vegetables in the roasting tin. If using a stock cube, pour over the water and crumble the cube directly over the vegetables.

Roast the lamb in the oven for 35 minutes per 500g.

Remove from the oven and allow the lamb to rest for 30 minutes before carving.

Serve the lamb with the roasted vegetables and spoon over the delicious roasting juices.