To make the pastry put the flour, butter and salt into a food processor with the S-blade. Whizz until the butter is well incorporated
If you don't have a food processor, put the ingredients into a large bowl and rub the butter between your fingertips until you have a sandy texture with no visible lumps of butter
Add small increments of water at a time until you have a soft, slightly sticky dough. Wrap the dough in foil, paper or cling film and put in the fridge while you make the filling
Preheat your oven to 170 Fan / 190 C / 375 F / Gas 5
For the filling, boil the potatoes for 15 or so minutes until they're just soft in the centre. Once done, drain and refresh in some cold water until they're cool enough to handle
While the potatoes are cooking saute the onion in a little butter and oil for 8-10 minutes, stirring often, until soft and transparent. Stir in the garlic then the mustard and herbs
Stir in the flour and mix well until everything's coated and looking a little dry! Then stir in the milk in 2-3 stages until you have a thick, silky sauce
Add in the nutritional yeast, bouillon powder, seasoning, grated cheese and mix well
Slice or dice the cooled potatoes and stir into the sauce. Set aside to cool
Cut about 1/3 of the pastry off and set aside. Roll out the larger piece of dough into a circle large enough to cover the base and sides of your 10 inch (25cm) loose bottomed pie tin
Carefully lift into the tin and push the pastry into the corners and sides. Trim off the excess pastry with a sharp knife - keep the scraps and use them to decorate the top!
Prick a few holes all over the base of the pie with a fork
Tip the cheese and onion filling into the pie and level so reasonably flat. Brush a little milk around the edge of the pastry that the lid will be sitting on
Roll out the 1/3 piece of reserved pastry large enough to cover the pie and again carefully lift it onto the pie and trim off the excess. Gently press the two pastry edges together. Slash a couple of holes in the centre of the pie lid
Roll out any trimmings and use whatever cutters you have to cut shapes. Brush the top of the pie with milk (you can add a little turmeric to the milk if you want an extra golden pie crust) and attach the shapes. Brush those shapes with milk too
Bake for 40-45 minutes until the pastry is crisp and golden. Allow to cool for a few minutes before cutting into portions and serving
Notes
Any leftovers can be chilled and stored in the fridge. I love this pie for a delicious savoury lunch with a crisp salad. It's also great picnic food!
Recipe by The Cook & Him at https://thecookandhim.com/recipes/cheese-and-onion-pie/