Put chopped carrot, onion, bay leaf and peppercorns into a pot lay the sweetbreads on top. Sprinkle with a little salt, add vinegar and cover with water. Bring up to the boil and simmer for 5 minutes only, allow to cool in liquor. Trim carefully, take off only the hard bits and allow to keep together in one piece.
Trim the lamb, leave some fat on. Heat oil then add the butter. Seal and colour the lamb on the outside, season and put into the oven 210c.
Meanwhile put potatoes to boil in jackets. Take out the lamb and allow to rest, pour off excess fat and add quarter of the shallots. Fry to colour and add the white wine except 1 tbsp. Reduce by half and strain into clean pot. Add rest of shallots and stock and allow to simmer away slowly. Mix 1tbsp white wine with the mustard and brush the outside of the lamb. Roll the lamb in chives.
Strain and drain the potatoes and crush mix with capers and olive oil and season.
Break sweetbreads into nugget sized pieces, roll in flour, shake off excess, dip in beaten egg and then dip carefully into breadcrumbs mixed with mint. Roll to keep breadcrumbs on. Fry in oil and butter golden brown and take out and drain on paper, keep warm.
If you want to be posh, put the hot potato mixture into a 2 ½inch ring on centre of plate; you can use a spoon if you prefer.
Slice the lamb and lay 3 slices on top of potatoes round one edge and 3 round the other. Pile the sweetbreads in the middle of lamb. Add butter to sauce and shake in, check seasoning and add parsley and serve round the dish.