Peel 200g (7oz) potatoes and cut into 2cm (1in) cubes. Place in a saucepan and cover with water. Bring to the boil. Salt the water and cook the potatoes gently for about 10 minutes or until there is no resistance when a sharp knife is inserted. Strain the potatoes and set aside to cool.
Thinly slice 1-2 red onions. Place a knob of butter and 2 teaspoon of oil into the frying pan and set over a medium heat. Add the sliced onions to the frying pan. Reduce the heat and cook the onions slowly until translucent and soft about 15 minutes. Once cooked tip onto a sheet of kitchen roll to absorb the excess oil.
Meanwhile, make the pastry. Place the 225g (8oz)flour, 50g (2oz) butter and 50g (2oz) lard or vegetable fat into bowl and rub in the fat with your finger tips until the mixture resembles bread crumbs.
Make a well in the centre and add the water, a little at a time. Using a rounded pallet knife, or similar, cut through the mixture to make a dough. You may not need all of the water. Bring the dough together with your hands and shape into a ball and flatten into a disc. Wrap in cling film and place into the fridge for 30 minutes to chill.
Preheat the oven to 200℃ (180℃ fan)/400°F/gas mark 6.
Cut the pastry into two equal pieces and roll out one piece and use to line the base of the pie plate. Roll out the remaining pastry for the pie lid.
Combine the cooked potatoes with the onions and season to taste with salt and pepper.
Grate 175g (6oz) Lancashire cheese and place half of the grated cheese into the pastry case. Add the potato and onion mixture. Top with the remaining cheese.
Using a pastry brush, paint the edge of the pastry with a little milk. Use a rolling pin to lift the rolled out pastry and lay over the filled pie plate. gently press the edges together to seal and trim away the excess pastry. Brush the top with a little milk and cut a small slit in the middle to allow steam to escape.
Bake the pie in the oven and bake for 30 - 35 minutes until the pastry is cooked through and a beautiful golden colour. You may need to rotate the pie halfway through the bake. Remove from the oven once cooked and allow to cool for 5 minutes before cutting into it and serving.