1. Preheat the oven to 220 C/450F/ Gas Mark 8.
2. Use a small pointed knife to make incisions into the lamb then tuck a sliver of garlic and a few rosemary leaves into each incision. Push the rosemary and garlic as far as possible into the lamb.
3. Put the lamb in a roasting pan and season with salt and pepper, then drizzle over the oil.
4. Roast for 20 minutes, then reduce the oven temperature to 190C/375F/Gas Mark 5, and roast for a further hour (add an extra 20 minutes for well-done lamb).
5. Remove from the oven, cover and leave to rest in a warm place for 20 minutes before carving.
6. To make a thin gravy to serve with the lamb, pour off the fat from the roasting tin then put it over a medium heat on the hob.
7. Add the red wine and boil, stirring with a wooden spoon to dissolve the browned residue in the bottom of the tin (this will help to flavour the gravy).
8. When the wine has almost evaporated add the stock and boil until reduced by about one third in volume. Taste and if the gravy isn’t quite flavourful enough, then boil for a couple more minutes.
9. Strain into a jug and serve with the lamb and roast potatoes.

To make the roast potatoes

1. Chop or crush 3/4 of the rosemary leaves and mix with the oils in a large bowl. If possible, leave to infuse for 1 hour.
2. Preheat the oven to 190C/375F/Gas Mark 5. Toss the potatoes in the oil then transfer to a roasting pan that will hold them in one single layer. Drizzle over any oil left in the bowl.
3. Roast the potatoes for 45 minutes, turning over halfway through. Meanwhile finely chop the remaining rosemary leaves.
4. When the potatoes are browned, crispy and tender remove from the pan with a slotted spoon and sit on a clean baking sheet. Sprinkle with salt and the rosemary before serving.