- Make the pastry first. Mix the flour, baking powder, salt, butter and egg yolk together until they resemble breadcrumbs. Add the Parmesan, mix well. Gradually add the water until the mixture comes together (not using all the water necessarily). Form into a ball, wrap in cling film then place in fridge about an hour.
- Peal and chop the potatoes into small squares. Bring a pan of salted water to the boil, add the potatoes and simmer for about ten minutes or until tender. Drain and wash under cold water to cease the cooking process.
- Meanwhile, heat butter in heavy bottomed pan over a low to medium heat. Add the onions and leek and gently fry for fifteen to twenty minutes, until soft and translucent.
- Turn up to a medium heat, add cream and milk and stir until the sauce has thickened slightly. Add the Lancashire cheese, potatoes and season well with salt and black pepper.
- You can then leave the mixture to cool while you prepare the pie case.
- Preheat the oven to 180C (fan), grease a pie tin with removable bottom. Roll out the pastry on a floured work surface nearly twice the size of the pie dish. Cover the pie dish with the rolled out pastry and press into the edges. Place some tin foil in the pie dish and add some beans so you can blind bake for fifteen minutes or until a pale golden brown colour. Remove from the oven.
- Once cooled, add the filling, then roll out a lid from the remaining pastry. Brushing the rim of the pastry case will allow you to 'glue' the lid on. Gently press the lid into place, make two incisions in the top to allow the steam to escape. Brush the top with beaten egg and then bake for about 30 minutes.
Recipe adapted from the BBC and Guardian.