1) Pre-heat the oven to 180C. Depending on if you have time to allow the potatoes and filling to cool, see step 7. 2) Bring a pan of water to boil. Add the potatoes and simmer for 15 – 20 minutes until cooked. 3) Drain the potatoes, add the soya milk and mash. Season to taste. 4) While the potatoes are cooking, put the rapeseed oil in a pan over a medium heat and sauté the onions and mushrooms for a few minutes until softened. 4) Add the chestnuts, soya mince, yeast extract, tomato puree and seasoning, stirring well to combine. 5) Add approx 150 - 200ml of water to loosen the mix and form a gravy. Again stir well to combine. 6) Pour your pie filling in the base of your baking dish. 7) If you have time, allow both the potatoes and the filling to cool. 8) Preheat oven to 180 C, 10 minutes before you are ready to compile the pie. 9) Dollop the potatoes roughly on top of the filling making as many peaks as you can for crisping up in the oven. 10) Bake in the oven for 30 minutes or until golden on top. 11) Allow to cool slightly before serving.