For the pastry, sift the flour into a bowl and season with salt and freshly ground black pepper.
Warm the milk, 50ml/2fl oz warm water and lard in a pan until the lard has melted. Bring just to the boil and pour onto the flour. Stir well until a dough forms. Turn the mixture onto a floured surface and knead for 3-4 minutes.
Roll the dough out to cover a 20cm/8in spring-form cake tin, saving extra pastry for the lid. Push the pastry into the tin to cover up any cracks. It is not a problem if the pastry doesn't cover the tin with the first attempt.
For the filling, place all the ingredients into a large bowl and mix until well combined. Place the filling into the pastry-lined tin.
Brush beaten egg around the rim of the pie and cover the filling with a pastry lid. Cut out a crown shape from the remaining pastry and place on top of the lid, securing with egg wash. Cut a hole in the pastry lid for the hot air to escape.
Brush the pie with egg wash, then cover with aluminum foil and bake in the oven for 1½ hours.
Allow the pie to cool and serve with leek and cream mash.