Preheat the oven to 200°C/400°F/gas mark 6. Place the soaked chestnuts, herbs and 170 ml of the wine in a saucepan with just enough vegetable stock to cover and cook until just tender (about one hour). Drain the chestnuts, keeping the liquid.
Melt the butter in a frying pan and sauté the onions on a low heat until slightly browned.
Add the mushrooms and cook for a further five minutes.
Add the chestnuts, the remaining red wine and sufficient chestnut cooking liquor to cover. Bring to the boil and simmer for 20 – 30 minutes to reduce the liquid a little.
Stir in the mustard, soy sauce and black pepper to taste. Cook for a further five minutes. Check the seasoning and adjust as necessary.
Spoon the mixture into a pie dish. Roll out the pastry on a floured surface and place on top of the filling. Bake for about 20 minutes until a golden crust forms.