Pre heat oven on gas mark 6 and put a baking tray in the centre of the oven
Flour work surface and rolling pin and roll out puff pastry till its about the same thickness of about 5 mm
Take a 8 inch x 5 inch pie dish and rub some butter inside greasing it lightly,then take your pastry and line the tin with it making sure to gently press it into the corners of the tin,trim the pastry but try to leave a small amount hanging over the sides of the pie dish
Grate 200 g of mature cheese into a mixing bowl,then finely chop 2 onions and also place into the mixing bowl,add 25 g of soft butter,give the mixture a good twist of black pepper,and mix it all in
Place the pie filling into your pie dish,and take your pastry lid and place on top,crimp the sides of the pastry together and take a knife and put 2 small slits in to the top of the pie,take an egg and mix it,then brush the top of the pie
Place in the oven on the baking tray and leave for 45 min until golden brown. Leave pie for 20 mins to cool after removing from oven.