Instructions

1. Take the lamb out of the fridge at least 30 minutes before preparation.
2. Score the meat all over, making 2cm deep incisions.
3. Cut each garlic clove into 4 pieces and push these into many cuts.
4. Put the pesto, oil, mint leaves, lemon juice and zest into a small food processor and whiz until you get a coarse paste.
5. Rub the meat all over with this paste pushing some into the remaining cuts with your finger.
6. Put the lamb on a rack, placed in a large roasting tray.
7. Pour some wine, stock or water into the tray then add the onion.
8. Preheat the oven to 180°C.
9. Roast the lamb for 1 hour, then cover with foil and roast for another hour or so ( calculate 25 minutes per 500g , plus 25 minutes for medium or 35-40 minutes for well-done).
10. Take the lamb out of the oven and transfer it to a plate.
11. Cover with foil and tea towels, then rest for about 20 minutes before carving.
12. Meanwhile, make the mint gremolata, by finely chopping the mint leaves and garlic and mixing together with lemon zest and a drop of lemon juice. Also, make some gravy from the roasting jus.
13. Serve the lamb with the mint gremolata and the gravy, together with side dishes.