For the filling, heat a splash of oil in a heavy-based casserole and fry the venison in batches, seasoning as you go, until golden brown. Transfer to a plate and set aside.
Add a splash more oil to the pan, add the bacon and fry for 5 minutes until golden. Add the onions and juniper, fry for 5 minutes until softened then stir in the garlic, thyme and bay leaves. Stir in the flour, fry for a minute then pour in the wine, stock and prunes.
Return the venison to the pan, bring to the boil then reduce the heat to a gentle simmer. Cover and cook for 2 hours, stirring occasionally, until the venison is soft and starting to fall apart. Leave to cool to room temperature.
Preheat the oven to 180ºC. Tip the flour into a large bowl and make a well in the centre. Put the lard into a saucepan with the salt and water and bring to a simmer. When the lard has melted pour the mixture into the well and stir to combine.
When the dough is cool enough to handle turn it out onto a lightly floured surface and knead into a smooth ball. Roll two thirds of the dough into a large disc, the thickness of a pound coin.
Line the cake tin with the pastry, leaving a couple of centimetres overlapping the edge of the tin. Spoon the cooled mixture into the pastry case and smooth down with the back of a spoon.
Roll out the remaining pastry to make the lid, glaze the inside of the dough with the beaten egg and lay the lid on top. Press the edges together to seal then trim away the excess pastry.
At this stage either leave the top if the pie plain, or use the excess pastry to make decorations for the top of the pie. Cut a steam hole in the top of the pie then cover loosely with foil and bake for two hours.
Remove from the oven, leave to cool slightly then carefully remove from the tin.
Sit the pie on a heavy baking tray, brush all over with the egg wash and return to the oven for 15-20 minutes until golden brown.