Slow-cooked lamb shank shepherd’s pie

Method

1. Heat the oven to 150°C/130°C fan/gas 2. Heat 3 tbsp of the olive oil in a large frying or sauté pan over a medium heat. Toss the lamb shanks in the flour to coat, then shake off the excess (reserve the flour). Brown the lamb shanks 2 at a time, then remove.
2. Meanwhile, heat the glug of oil in the casserole over a medium heat, then add the onions, celery and carrots. Cook, covered, for 10 minutes, until softened. Stir in the garlic and 2 tbsp of the reserved flour. Cook for 3 minutes, then stir in the tomatoes and cook for 2 minutes more.
3. Turn up the heat, pour in the wine, stir, then tuck in the lamb shanks and stir in the Worcestershire sauce, bay leaves and rosemary. Bring to a simmer, put the lid on and cook in the oven for 2½-3 hours or until the lamb is tender and pulls away easily from the bone. Turn the shanks twice during cooking so they cook evenly.
4. Remove the shanks from the casserole and set aside. If the stock hasn’t reduced enough during cooking, put the casserole on the hob and simmer briskly, uncovered, for 10 minutes or so. Use a couple of forks to strip the meat from the bones, keeping it in large chunks (keep one bone to poke out of the pie top for decoration, if you like). Return the meat to the sauce, then pour into the baking dish (or see Make Ahead).
5. Turn the oven up to 200°C/180°C fan/gas 6. Grate the potatoes coarsely using a box grater. Wrap up tightly in a large clean tea towel, then squeeze to remove as much water as possible. In a bowl, toss the potatoes with the leek and the remaining 2 tbsp olive oil, then season with ½ tsp salt and toss again to coat evenly.
6. Spread the rösti topping on top of the lamb, then bake for 40 minutes until the topping is crisp. Scatter over the cheese, then bake for 5-10 minutes to melt and turn golden. Serve with extra steamed veg.