`Venison and Chestnut Pie

25g/1oz plain flour
900g/2lb diced venison5 tablespoons sunflower oil
25g/1oz butter
225g/8oz small chestnut mushrooms
2 onions, halved and sliced
1 tablespoon sugar
4 garlic cloves, crushed
300ml/10fl oz beef or game stock
300ml/10fl oz port or red wine
1 teaspoon tomato puree
The leaves from 3 sprigs of thyme
1 heaped tsp crushed juniper berries
500g/1lb chilled puff pastry
1 egg, beaten, to glaze

100g/4oz vacuum cooked & peeled chestnuts
Salt & ground black pepper

Season the flour with salt and pepper, put into a bowl with the venison and toss together well until all the pieces are coated.
Heat 3 tablespoons of the oil in a large, flameproof casserole, add half the venison and fry over a high heat until browned. Lift onto a plate and repeat with the rest of the venison. Set aside.
Add half the butter and the mushrooms to the pan and fry briskly over a high heat for 2 minutes. Set aside with the venison. Add the rest of the oil and butter, onions and sugar to the casserole and cook over a medium-high heat for 20 minutes, stirring frequently, until nicely browned. Add the garlic and cook for 1 minute.
Stir any remaining flour into the onions, followed by the stock, port or red wine, tomato puree, thyme leaves and juniper berries and bring to the boil, stirring. Return the venison and mushrooms to the pan, season with salt and pepper, part-cover and simmer for 1 1/2 hours until the venison is just tender, and the sauce has reduced and thickened. Leave to go cold and then stir in the chestnuts.
Roll out the pastry on a lightly floured surface and then put a 1.75 litre/3-pint pie dish upside down into the centre. Cut out a lid, which is 2.5cm/1inch larger than the top of the dish and then cut a small cross in the centre.
Spoon the filling into the pie and brush both the underside and the top of the rim with a little of the beaten egg. Lay over the pastry so that the funnel pokes through the cross and press the edge of the pastry well onto the top and underside of the rim to make a good seal. Chill for 30 minutes.
Preheat the oven to 200C/400F/Gas Mark 6. Brush the top of the pie with beaten egg and bake for 30-35 minutes until the top is golden and the filling is bubbling hot.