Take the lamb from its wrapping. Pat dry with kitchen paper. Peel and finely slice the onion. Arrange the onion in a small roasting dish. Rest the lamb on top and let it get to room temperature. Heat your oven to 220°C/Fan 200°C/Gas 7.
Tip the juniper berries into a pestle and mortar. Crush till all the berries have split open. Strip half the leaves from the rosemary. Add to the mortar with a good pinch of salt and pepper. Add 1 tbsp olive oil and muddle together. No pestle and mortar? Crush everything in a jam jar with the end of a rolling pin.
Using a sharp knife, make small deep incisions in the lamb, including the ends. Rub the juniper and rosemary marinade all over the lamb, pushing some into the incisions.
Roast the lamb in the oven for 25 mins, then take out of the oven. Tip away the fat if you like (take care to keep all the flavourings on the lamb). Turn the oven down to 160°C/Fan 140°C/Gas 3.
Add the remaining rosemary leaves to the dish. Pour a mug of water, vegetable or chicken stock, or white wine around the lamb. Cover the lamb with a double layer of foil. Cook for 3 hrs. The lamb should be meltingly soft and tender.
Remove from the oven and place the lamb on a board. Cover and leave to rest for at least 30 mins. Reheat the pan juices and serve with the carved lamb.
Whip up our Lamb & Caramelised Onion Flatbreads. Find the recipe at abelandcole.co.uk/recipes