Preheat the oven to 190 C / 375 F / 170 FAN / Gas 5.

Bring the meat to room temperature for about an hour before cooking, then season with the salt and pepper.

Peel the onion and cut into 1 cm slices, rough chop the celery and carrots and slice the garlic across the cloves.

Arrange the vegetables in the base of a large roasting dish, along with the rosemary and juniper berries.

Place the leg of mutton on top.

Roast for 2 hours and 30 minutes. Check the internal temperature for 65 degrees.

Transfer the meat to a large plate and cover with foil to rest for at least 20 minutes up to an hour.

Remove the rosemary and juniper and discard.

Use a slotted spoon to remove the vegetables and place in a blender or a saucepan if you are using a hand blender. Squeeze out the roasted garlic and discard the skin.

Remove nearly all of the fat from the roasting tin and add the hot stock to deglaze the pan.

Pour the stock into the saucepan or blender along with the cornflour and redcurrant jelly and blend until smooth.

Bring to the boil in a saucepan and simmer until it reaches your desired consistency, adding more water if required.

Slice the mutton and serve with the gravy.