Preheat the oven to 220°C/200°C fan oven/Gas Mark 7. Cook the leeks in a large pan of boiling salted water for 2 to 3 minutes or until just beginning to soften. Drain, reserving the cooking liquid. Plunge the leeks into cold water, drain and dry very well on kitchen paper or spin in a salad spinner.

Melt the butter in a large pan, take off the heat and mix in the flour to form a smooth paste. Mix in 450 ml (15 fl oz) leek water and the milk, stirring until smooth. Bring to the boil, simmer for 1 to 2 minutes, cover and cool for 20 minutes or until cold. Add the marjoram, leeks, the cheese and ham and season with salt and pepper.

On a lightly floured surface, roll out one sheet of puff pastry to a rectangle measuring 30.5 x 33cm (12 x 13 in). Cut into two rectangles, one measuring 15 x 30.5cm (6 x 12 in) and the other one measuring 18 x 30 cm (7 x 12 in). Repeat with the other sheet of pastry.

Take the smaller rectangles and put them on two greased baking sheets. Spoon on the ham mixture, leaving a 2 cm (3/4 in) pastry border all the way round. Brush the edges of the pastry with the beaten egg. Cover the filling with the larger rectangles of pastry and press the edges together firmly. Cut several slashes in the top of the pastry to prevent the filling seeping out while the galette is cooking. Crimp the edges of the pastry to seal, then cover and freeze for 20 minutes until firm.

Remove from the freezer, brush all over again with the beaten egg, make a good-sized steam hole in the centre of each parcel and sprinkle with the grated cheese.

Bake the galettes for 20 to 30 minutes or until brown and crisp.

Freezing: At the end of step 4, cover in clingfilm and freeze on the baking tray. When firm, remove from baking tray. Wrap in baking parchment, then in clingfilm.

To serve: Defrost for 3 hours at room temperature on baking parchment. Put a flat baking tray in the oven to

preheat to 220°C/200°C fan oven/Gas Mark 7 and complete step 5 of recipe. Put galette on the hot tray (this will keep the pastry base crisp) and bake for 40 minutes.