The juices from slowly roasting lamb drip into potatoes and onions in this hearty dinner, served with a sharp mint sauce.
For the mint-stuffed lamb shoulder, preheat the oven to 170C/340F/Gas 3½.
Heat a frying pan and add the butter. Once hot, add the onion and garlic and cook for 3-4 minutes until soft.
Put the onion and garlic in a bowl and allow to cool, then add the rest of the ingredients, apart from the lamb shoulder, and mix together to make stuffing.
Place the lamb shoulder on a board and spread the mint stuffing inside the lamb. Roll up and tie with kitchen string.
Place the lamb directly on the rack in the oven and cook for one hour while you prepare the potatoes.
For the boulangère potatoes, mix the potatoes and onions in a bowl and season with salt and pepper.
Use the butter to cover the bottom of a deep baking tin. Layer the potatoes and onions on top and pour over the stock.
Put the roasting tin on a low shelf in the oven and place the lamb directly on the shelf immediately above - so that the juices will drip onto the potatoes.
Cook the lamb and potatoes for another two hours.
For the mint sauce, put the chopped mint into a small bowl.
Heat the vinegar and sugar in a saucepan until simmering and pour the mixture onto the mint. Stir until well combined.
To serve, carve the lamb shoulder and place on a plate. Serve the potatoes alongside and pour over the mint sauce and lamb jus or gravy.
