Preheat the oven to 180C/350F/Gas 4. For the potatoes, melt 55g/2oz butter in an ovenproof frying pan. Add the potatoes and cook until golden brown. Turn over, add the stock and season with salt and freshly ground black pepper. Roast for 30-40 minutes, or until cooked through.
Trim the fat from the hogget and flatten the meat as thinly as possible.
Put the chicken through a mincer. Beat in the cream and sea purslane, then season with salt and freshly ground black pepper.
Lay the chicken mousse on the fat next to the meat and roll, ensuring the chicken is covered with only one layer of hogget. Trim off any excess fat. Tie evenly with butcher’s string and seal at each end with the bacon.
In a frying pan, sear the hogget in the oil, turning, for 5-7 minutes, until browned all over, rendering as much fat as possible. Transfer to a roasting tray, season and roast for 10-12 minutes, depending on size, until cooked through. Insert a skewer into the middle of the roast to ensure the juices are piping hot. Remove from the roasting tray and leave to rest in a warm place for 10 minutes.
For the cabbage, blanch the cabbage in boiling water for 20 seconds, then drain. Melt the butter in a large pan, add the cabbage and cook for 2-3 minutes. Add the parsley and sea purslane and season with salt and freshly ground black pepper.
For the gravy, while the hogget rests, pour away the excess fat from the roasting tray. Place the tray on the hob and add the onion, then cook until coloured. Add the stock and cook until the volume of the liquid is reduced by one third. Beat in the butter and season with salt and freshly ground black pepper.
To serve, melt the remaining 15g/1/2oz butter and brush it over the potatoes. Remove the bacon and string from the hogget and serve the meats with the potatoes, cabbage and gravy.