Pre-heat the to Oven: 180°C/ 350°F/Gas 4, and 160°C/ 325°F/Gas 3 or Fan oven: 160°C and 150°C.

To make the stuffing, heat the oil and butter together in a saucepan. Add the red onion and garlic and over a low heat cook until softened, but not coloured. Remove the pan from the heat and stir in all the remaining stuffing ingredients with some salt and pepper. Cool.

Lay the boned leg of lamb on a board (skin side down). Press the stuffing over as much of the cut surface as possible. Bring the meat edges over the stuffing so that it is as enclosed as possible. Tie the joint into a neat shape with several bands of fine string. Rub oil evenly over the outside of the meat and season well with salt and pepper.

Oil the inside of the Le Creuset Signature Cast Iron Oval Casserole. Heat on the stovetop over a medium heat setting. Add the lamb and brown evenly all over. Cover with the lid and transfer to the oven (there is no need to add any liquid). Roast for 30 minutes at the higher setting before reducing the temperature and roasting for 2 hours at the lower setting.

Lift out the lamb and allow it to rest for 15 minutes. Cover securely to keep it hot.

Drain off all but two tablespoons of liquids and residues from the casserole. Transfer the casserole to the stovetop adding the wine and stock, bring this to a boil. Blend the softened butter and flour together (a beurre manié) and drop small amounts of this into the hot liquid. Whisk each amount in so that it becomes thoroughly blended and thickens the sauce. Add the berries and cherries conserve, stirring until it melts into the sauce. Season to taste.

Remove the strings from the lamb and slice the meat thickly. Serve with a little of the sauce poured over and the rest separately.