Sift pastry flour into a bowl and rub in lard and butter until resembling breadcrumbs.
Mix in salt, baking powder, and 4 tablespoons water to form a soft dough.
Knead the dough into a ball, wrap in film, and chill in the fridge.
Preheat the oven to 180°C.
Combine all filling ingredients in a large mixing bowl.
Line a 900g loaf tin with baking parchment.
Roll out two thirds of the pastry and line the bottom and sides of the tin.
Spoon the filling into the tin and press down firmly to compress.
Roll out remaining pastry to create a lid and seal the edges with water.
Trim and crimp edges with a fork and decorate the top with a pastry bow.
Glaze the top with beaten egg and bake for two hours.
Cool completely in the tin before turning out.