Sweet Potato Shepherd’s Pie

Place a large pan over a medium flame and heat the oil briefly, then lower the heat, add the onion and cook for about five minutes until the onion has softened but not coloured. Add the minced lamb, carrots and leeks and cook together until the meat is well browned all over. Add the thyme and parsley to the pan, stir in the flour and then pour the stock into the pan in a steady stream, stirring all the while. Stir in the tomato purée, then reduce the heat, cover the pan and simmer for about 30 minutes, stirring occasionally.

While the meat is cooking, peel the sweet potatoes and cut them into evenly-sized chunks. Bring a pan of water up to the boil, then cook the sweet potatoes for about 10 minutes, until just tender. Drain the potatoes and return them to the pan, away from the heat, then add the butter and mash until smooth. Sprinkle in the nutmeg or mace, season with salt and pepper to taste and set aside. When the mince mixture is cooked, season to taste with salt and pepper and spoon into a large, oven-proof dish. Spread the mashed sweet potato carefully over the meat, then scatter the grated cheese evenly over the top of the potato. Bake for about 30 minutes at 200°C (Gas Mark 6) or until the top is nicely browned and the pie is piping hot throughout.