The stew can be made in advance and topped with potatoes and baked on the day you want to eat it – perfect for a midweek meal.
Heat the oil in a heavy-bottomed pan. Add the lamb and cook until golden-brown and then stir in the tomato purée.
Add the stock and simmer for 2-3 hours, or until the lamb is tender.
Add the onion, carrots and celery and cook until the vegetables are soft.
Season to taste with salt and pepper. Add the mint and cook for 2-3 minutes. If necessary, thicken the sauce by adding the cornflour paste.
Preheat the oven to 180C/350F/Gas 4.
Transfer the stew to an ovenproof dish. Place the sliced potatoes on top and brush with melted butter. Bake for 30 minutes, or until the potato topping is golden-brown.
Sprinkle with dried parsley and serve with gravy.
