Knead flour, butter, egg and salt, or process in the food processor, till smooth. Cover and let refrigerate for at least 30 minutes.
Preheat your oven to 200 C / Gas 6.
For the filling cut leeks in half and wash thoroughly. Cut into 1cm slices and blanch for 1 minute in boiling water. Drain and rinse under cold water, let drain well, and gently squeeze out any excess water.
In a bowl whisk cream, eggs and cheese and season with a little bit of salt, pepper and nutmeg.
Grease a 26cm pie or tart tin. Roll out the pastry on a lightly floured work surface to fit the tin and let the pastry come up the sides. Prick the bottom several times with a fork.
In a bowl mix leek and ham and distribute half over the pastry. Pour half of the egg mixture on top, then repeat this with the rest of the filling.
Bake on the lower rack of your oven till the filling it set and lightly browned. If the top gets too dark, over with greaseproof paper. Let rest for 10 minutes after baking before cutting.