Peel off the potatoes, soak into salted water, bring to the boil and simmer for at least 20 minutes. They are ready when they’re tender (pierce with a knife). Drain and set aside.
Prep the filling: soak the textured soy proteins for 10mn in boiling water. Meanwhile, mince the onion and garlic. Drain the soy proteins. In a large pan, heat the olive oil and sauté the onion and garlic for 5 minutes on medium heat, then add the miso paste, soy sauce and tomato purée. Stir well, add the soy protein and sauté for another 5 minutes.
Meanwhile, prepare your topping. Mash the potatoes and stir with the milk, soy cream, nutritional yeast and mustard. Salt to taste and set aside.
Preheat oven to 200°C (392°C). Pour the filling in a baking tin. Cover in mashed potatoes and bake for 10 minutes, then broil for 5 minutes. Your pie is ready when the potatoes show grilled golden-brown peaks.