Place the sea vegetables in a large heatproof bowl and cover with boiling water. Leave to rehydrate for at least 20 minutes.
Boil and mash the potatoes. (See tip number 4 above!) Set 500g aside to cool.
Heat the oil in a pan. Add the onion, garlic and leeks and sauté for approximately 15 minutes until all the vegetables are soft.
Rinse and drain the sea vegetables and dry off in a clean tea towel.
Roughly chop the sea vegetables – just enough to ensure there are no very long, stringy pieces, and place in the food processor along with the onion mixture, miso paste, lemon zest, salt, pepper and dill. Process until the sea veg is broken down into small pieces.
Combine the sea veg mixture and the mashed potato in a large bowl. Taste and add seasoning if needed. Refrigerate for an hour or so (it will be easier to work with when it has been chilled for a while).
Put the mustard into a small bowl. Gradually add the soya milk, stirring constantly as the milk thickens. Place the breadcrumbs in another bowl.
Use your hands to form the potato cakes, and one by one, dip them into the milk/mustard mixture – shaking gently to remove any excess – and then roll in the breadcrumbs until covered on all sides.
Cover the base of a frying pan with sunflower oil and put on a medium heat. When the pan is hot, carefully slide the potato cakes into the pan. Fry on each side for 4-7 minutes until golden. Remove from the pan and place on a plate lined with kitchen paper to absorb any excess oil.
Serve warm with rocket or mixed leaves and dill and chive sour cream – recipe to follow!