Start with cooking the potatoes. After you’ve peeled the skin off, 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.
Meanwhile prepare the filling. Mince the onion, garlic and mushrooms and cut your seituna with multi-blade kitchen scissors. In a large pan, heat the olive oil and sauté the onion and garlic for 5 minutes on medium heat, then add the mushrooms and seituna. Sauté for another 5 minutes, then add the white wine, crushed nori seaweed, half of the milk and half of the soy cream. Simmer for 10-15mn.
Meanwhile, prepare your topping. Mash the potatoes and stir with half the milk, half the cream, nutritional yeast and mustard. Salt to taste and set aside.
Preheat oven to 200°C (392°C). When the filling has thickened, add the petits pois, stir well and salt to taste. Pour 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.