Fry the onion for 5-8 mins until translucent and then add the pressed and cubed tofu. Allow to fry for a few minutes to seal and then add the garlic and mushrooms. Continue to fry on a medium heat until all the juices of the mushrooms are released. Add the flour and mix carefully until everything is coated and there’s no lumps of flour. Add the soya milk gradually and stir continually until all the milk is absorbed each time. When you have a thick sauce, add the mustard, nutritional yeast and season with sea salt and freshly ground black pepper.
Fill the pastry case and cover with the pie lid. Make a hole in the lid for the steam to escape. You may want to brush the top of the pie lid with a little milk to give the crust some colour.
Bake at 180 deg C (350 deg F) for 30-35 mins or until the pie case has browned on top.