Wash the potatoes and steam until tender. Spear them with a carving fork and peel while still boiling hot. Push them through the potato ricer while still hot; repeat the ricing operation, and then finally push them through a fine sieve into a large bowl.

Preheat the oven to 350°F (180°C) mark 4.

Heat the milk together with 2 oz (60 g) of the butter and a little salt and freshly ground pepper until scalding. Stir most of the milk into the sieved potato; work in the eggs, Parmesan cheese and the finely grated rind of the lemon.

The mixture should be fairly soft; add the rest of the milk if necessary. Stir this mixture thoroughly for 2 minutes, then add the smoked cheese, the chopped Mortadella or ham and the basil.

Grease a cake tin about 9 1/2 in (24 cm) in diameter and at least 2 in (5 cm) deep. Place a quarter of the mixture in the tin and press out flat into an even layer with the palm of your hand.

Spread out 6 slices of mozzarella on the surface and cover with another quarter of the mixture. Repeat these last two layers. Spread the sausage slices on top. Sprinkle breadcrumbs over the surface and dot small flakes of the remaining butter on top.

Bake for about 30 minutes, browning under a very hot grill for a final 5 minutes to form a crisp topping.