Preheat the oven to 160°C
Layer the potatoes and onions in a baking dish and place the lamb on top
Slice across the lamb about 1cm deep
Mix the glaze 1 ingredients together and brush all over the lamb getting into all the cuts
Pour the stock all round the lamb and over the potatoes
Cover tightly with foil and put in the oven for 4-5 hours until tender
Remove from the oven and turn the oven temperature up to 180°C
Mix the glaze 2 ingredients together and brush the lamb with glaze
Baste any dry looking potatoes with some of the lamb fat from the dish
Return to the oven without the foil for 20-30 minutes until the top of the lamb and potatoes are golden
Serve with peas and red wine sauce or on its own
