- 1 large onion, cut into thin rings
- 75 g (1/2 cup) pine nuts
- 2 tbs Parmesan, grated
- 2 cloves garlic
- 25 g (1 cup) basil leaves, plus extra garnish
- 25 g (1 cup) mint leaves, plus extra to garnish
- 2 tbs lemon juice
- 100 ml extra-virgin olive oil, plus 2 tbs extra for brushing
- 2 kg leg of lamb, on the bone, trimmed of excess fat, left to stand at room temperature for 1 hour
- Freshly ground black pepper
Preheat the oven to 220°C (200°C fan). Line a large roasting tray with a trivet large enough to hold the lamb. Scatter the onion rings on top of the trivet.
While the oven heats up, pulse together the pine nuts, Parmesan, and garlic in a food processor until the pine nuts are almost ground.
Add the herbs, lemon juice, and olive oil, pulsing several times until a thick pesto comes together. Season to taste with salt and pepper; cover and chill until needed.
Preheat a large sauté or frying pan over moderate heat until hot. Brush the leg of lamb with 2 tbsp olive oil and season with salt and pepper; transfer to the trivet, carefully positioning the lamb on top of the onion.
Roast the lamb for 30 minutes; reduce the oven to 180°C (160° fan). Roast for a further 1 hour 5-15 minutes until the thickest part of the leg registers 60°C on an instant-read thermometer for medium meat, basting with a little of the pesto after 45 minutes.
When ready, remove from the oven and loosely cover with aluminium foil; let rest for at least 15 minutes.
When ready to serve, garnish with more herbs and serve with the remaining pesto on the side.