Here you go, Rory (and I’m from Cheshire - born there, still live within the traditional county border)
A pie for six:
750g leeks, thinly sliced
300g mushrooms (whatever), sliced
2 garlic cloves
350g shortcrust pastry
200g chestnut pieces ( vac pack or tinned)
150ml creme fraiche
Melt the butter in a frying pan and soften the leeks for 10 minutes. Add the mushrooms, garlic parsley and thyme. Cook for 5 minutes more, then leave to cool.
Line a pie dish with half the pastry. Stir the creme fraiche and chestnuts into the cold leek mix. Add all but a bit of the eggs (beaten). Use the other half of the pastry to make a lid (and any pretty decoration with any offcuts). Give the top an eggwash with the remaining egg. Bake at 180c for about an hour (but check a bit before to make sure it’s not burning). Let it rest for 30 minutes or so - it’s dish for eating warm or cold, not hot straight from the oven.
If you try it, please let me know what you thought (particularly if you tweaked the recipe for the better)