Begin by pre-heating the oven to 180°C, and browning off the seitan in a non-stick pan with a little olive oil. Then add the mushrooms and onion, cooking over a medium heat until the onions are softened.
Add the flour and herbs, bay leaf, and salt and pepper and mix well. Add the mushroom gravy and stock. Turn the heat down to low-medium and let the mixture simmer for 10 minutes or so.
While the seitan mixture is simmering, roll out your shortcrust pastry and line your pie tin, sifting a little plain flour into the tin beforehand to prevent sticking.
Spoon the mixture into the pie tin, and then top with the remaining pastry. Make a few cuts in the top of the pie to allow steam to escape, and press the edges down with a fork. Lightly brush the top with soya milk.
Bake the pie at 180°C for around 40 minutes, or until golden brown.
Serve with your favourite potatoes (I like mashed) and veggies of your choice, along with lots of thick gravy (it’s got to be Bisto Onion for me).