Cook, mash and cool potato.
Chop herbs.
Mix all ingredients except the plain flour together and season with salt and pepper.
Add 1 tablespoon of plain flour at a time until you get a texture similar to mashed potato (I used 4 tablespoons this time).
Cover and refrigerate for 2-10 hours (until you need it).
Heat frying pan medium-high.
Add good splash olive oil.
Shape the chilled mixture into patties
Drop them gently into the hot oil. Leave plenty of space between them so they fry instead of steaming.
Don't touch them for the first few minutes. Let the sourdough and starch form a deep, golden crust. If you try to flip them too early, they will stick and tear. Give them about 3-4 minutes.
Carefully flip and cook the other side until golden brown, another 3-4 minutes.
Transfer to a wire rack and sprinkle with some flaky salt.
Use as a side dish for Fish, Steak or Chicken or just enjoy them on their own!