John Whaite's potato, cheese & onion pie

For the pastry put the flour, salt and butter into a bowl. Rub the butter through the flour until you have inelegant breadcrumbs. Make a well in the centre of the dry ingredients. In a small jug mix together the milk and vinegar, then add it all to the dry ingredients. Using a blunt knife, cut the milk into the flour until it starts to clump together. When it does (and most of the dry, powdery bits of flour are incorporated) knead the pastry briefly – no more than 20 seconds – until it is reasonably smooth. Flatten into a disc, wrap in clingfilm and chill for at least 30 minutes.

For the filling wash and quarter the potatoes – I don’t bother to peel them, but feel free if you prefer. You have two options here. The first, and my preferred method, is to set the potatoes and the quartered onion in a steamer above a pan of boiling water and cover with the lid. Steam the potatoes for 25 minutes, or until very easily pierced with a knife. The second option is to put the potatoes and quartered onion into a large pan and cover with cold water and a generous pinch of salt. Bring the water to the boil and cook the potatoes for 20-25 minutes, again until easily pierced with a knife. When the potatoes are cooked, either remove them from the steamer or drain them, then return them to the hot, dry pan and leave to steam for 5 minutes or so. Finely chop the boiled onion and add it to the pan.

When the potatoes have steamed add the remaining filling ingredients, stirring to combine, and seasoning to taste with salt and white pepper – some of the potatoes will fall apart, but don’t worry, just get it all evenly combined.

Preheat the oven to 200°C, gas mark 6, and place a baking sheet in the oven to heat up. Take two thirds of the pastry and roll it out on a well-floured worktop, until it forms a disc big enough to line the base of a 23cm pie dish, with surplus hanging over the sides. Pile the cooled potato mixture into the pie dish and level off with a spoon. Roll out the remaining pastry to a disc big enough to top the pie, again with a little excess, and place it on top of the potatoes. With a sharp knife, trim away the excess pastry, then crimp the pastry together at the edges.

Beat the egg yolk with a pinch of salt and a drop of water and use it to glaze the top of the pie. Cut a hole in the centre to let out steam. Place onto the hot baking sheet in the oven and bake for 30-35 minutes, until the pie is a deep golden brown. Allow to rest for 5 minutes or so before serving – this will help to set the filling.