Leek and walnut pie

This was an improvisation, and could be tweaked no doubt.

Ingredients
1 fat leek, the white part, sliced into rounds
1 fairly large shallot, finely chopped
some cubed pancetta - half of one of those twin packs Waitrose sell
2 small cloves of garlic, crushed and chopped
a handful of shelled walnuts, lightly chopped
some stock (I used the liquid from boiling chick peas)
about a tablespoon of plain flour
salt, pepper, a little allspice
some mashed potato
oil

Procedure
In a big saute pan heat the oil and add the pancetta, shallot and garlic. Fry gently until the shallot is soft.
Add the leeks and let them get hot.
Add the flour, stirring it into the oil. You might want to add some butter.
Before the flour goes brown, add the stock, and mix it into the flour. Keep stirring for a while. You're basically making a white sauce.
Season creatively and add the walnuts.
Let it all cook for about 10 minutes, adding more stock if it looks too dry.

Meanwhile, preheat your oven to 180c and prepare your mash.
Put your leek mix into a pie dish and dump the mash on top. Decorate it artistically with a fork, then bake for about 20 mins until the mash has browned a little.

Allow to cool a little before eating. If you can stand to wait, let the pie cool completely to room temperature and eat it with some kind of salad. (It was much nicer like this).

Possible tweaks would include leaving out the pancetta and adding cheese somewhere along the line.