For the tomato sauce, heat the olive oil in a small saucepan and saute the onion over moderate heat until it is soft and golden.

Add the canned tomatoes together with their juices, the dried basil, sugar and a little salt and freshly ground black pepper to taste - season lightly at this stage, bearing in mind that the sauce will reduce as it simmers. Simmer for 20 minutes until the sauce has thickened, stirring and mashing occasionally with a wooden spoon.

Rub the tomato sauce through a sieve and adjust the seasoning.

Meanwhile, reserve 4 of the potatoes in a bowl of cold water. Place the remaining potatoes in a pan of boiling, salted water and cook until tender. Drain well then return to the pan and mash with 75 g (3 oz) butter until quite smooth. Beat in the eggs and season to taste with salt and freshly ground black pepper. Leave to cool slightly.

Using a piping bag fitted with a 10 mm (1/2 in) nozzle pipe a border of mashed potato round a large shallow flameproof dish.

For the lamb hash, cut the remaining potatoes into 5 mm (1/4 in) dice. Blot well with absorbent paper. Heat 25 g (1 oz) of butter with half the oil in a large frying-pan and saute the diced potatoes for 5-7 minutes or until they are golden brown, shaking the pan and turning constantly with a spatula. Season with salt and pepper. Transfer the potatoes to a plate with a slotted spoon and keep warm.

In a large, deep frying-pan, heat the remaining butter and oil. Add the chopped onion and saute for 5 minutes, stirring occasionally, until the onions are soft. Add the diced lamb and saute for a further 5-7 minutes until the lamb is golden brown, stirring constantly. Season to taste. Heat the grill to high.

Add the cooked, diced potatoes and tomato sauce to the lamb and bring the mixture to a simmer. Correct the seasoning with salt and pepper. Pour the mixture into the centre of the piped potato. Sprinkle the lamb with Parmesan cheese and grill for 7—10 minutes until golden brown. Serve immediately.