Step 1

Heat the oven to 150°C/130°C fan/gas Heat the 3 tbsp oil in a large flameproof casserole over a medium heat. Toss the lamb shanks in the flour to coat well, then shake off the excess (reserve). Once the oil is shimmering hot, add the lamb in batches and brown all over. Remove them from the pan and set aside.

Step 2

Turn down the heat and pour away the fat in the pan. Add another large glug of oil to the casserole, then add the onions and celery. Cook over a low-medium heat for 10 minutes, stirring often, or until the veg is softened but not coloured. Stir in the garlic and 2 tbsp of the reserved flour. Cook for another 3 minutes, then stir in the tomato purée and cook for 2 minutes more.

Step 3

Turn up the heat, then add the wine and chopped tomatoes. Tuck in the lamb shanks, making sure they’re submerged. Stir in the bay leaves and carrots. Once the liquid begins to simmer, transfer the pot to the middle rack of the oven. Cook for 2½ hours or until the lamb is very tender and pulls away easily from the bone. Turn the shanks a couple of times during cooking so they tenderise evenly.

Step 4

Once the meat is cooked, remove the shanks from the casserole and set aside to cool. If the liquid isn’t quite thick enough (it should very lightly coat the back of a spoon), put the dish on the hob and simmer, uncovered, for 5-10 minutes. Strip the meat from the bones, keeping it in large chunks (discard the bones). Return the meat to the sauce and set aside.

Step 5

Increase the oven temperature to 200°C/180°C fan/gas Peel the potatoes and cut off the round edges  to form rectangles. Keep everything, including the off-cuts, in separate bowls of salted water. Slice each potato lengthways as thinly as you can (use a mandoline if you have one), then return the slices to the salted water while you slice the rest. Drain the potato slices and dry well on kitchen paper, then toss them in a bowl with the melted butter. Chop a large handful of the off-cuts into very thin slices, then stir them into the ragù.

Step 6

Transfer the ragù to a 2.5 litre wide, shallow ovenproof dish. Lay the potato slices in a right-angled, overlapping pattern over the top (you’ll get a couple of layers), then season well with salt. Bake for 
50 minutes or until golden. Serve with seasonal green veg.