Start by making the filling. Bring a saucepan of water to the boil. Peel the potatoes and cut them into slices about 3mm thick. Carefully drop these into the hot water and bring it back to the boil. Cook the potatoes for 3 minutes, then drain them in a colander and rinse them under cold running water until cool. Leave to drain.
Melt the butter in a large non-stick frying pan and fry the leek over a medium heat for 4–5 minutes until softened but not coloured, stirring regularly. Add the ham to the pan, toss lightly with the leek and remove from the heat. Leave to cool. Place a sturdy baking tray in the oven and preheat the oven to 200°C/Fan 180°C/Gas 6.
For the pastry, put the flour in a food processor and add the salt, crumbling it in your fingers as you do so. Drop the cubes of butter on top and blitz on the pulse setting until the mixture resembles fine breadcrumbs. Pour the egg and water on to the flour and butter mixture with the motor running and continue blending until the dough begins to form a ball.
Gather the pastry and turn it out on to a lightly floured surface, then knead it quickly into a ball.
Roll it out on a lightly floured surface until it is about 5mm thick and use it to line a 23cm loosebased tart tin. Press the pastry well into the base and sides and trim the edges.
Pour the cream into a jug and season with a good grating of nutmeg, plenty of salt and freshly ground black pepper. This pie can take a lot of seasoning. Arrange a layer of potatoes in the pastry case, top with a scattering of leeks and ham and a slurp of the seasoned cream. Repeat the layers twice more. Slowly pour the remaining cream mixture into the pastry case, stopping
every now and then to allow the cream to find its way between the layers.
Bake the pie on the preheated baking tray for 45–55 minutes until pale golden brown andcooked through. Test it is ready by piercing the centre of the pie with a sharp knife. The potatoes
should be very soft and the cream firm. Remove from the oven and leave to stand for 10 minutes before lifting from the tin. Serve warm or cold in wedges.