Nutrition: Per serving
Bring a pan of salted water to the boil and cook the potatoes for 10 mins.
Meanwhile, warm the milk over a medium heat in a saucepan until just simmering, this will take a few minutes. Remove from the heat, add the salmon and cover with a lid.
Drain the potatoes in a colander, then put the colander on top of the empty pan to steam for 5 mins.
Remove the salmon from the milk, reserving the milk. Add the lemon zest and juice, parsley, dill, cornichons and spring onions to the milk along with the sumac. Tip in the potatoes and roughly mash, then add the salmon, breaking it up into chunks, and mix everything together with some seasoning.
Tip the flour into a wide, shallow bowl, the beaten egg into another and the breadcrumbs into a third bowl. Using your hands, shape the salmon mixture into four fishcakes. Dip each fishcake into the flour to lightly coat, shake off any excess flour, then dip into the egg, and finally the breadcrumbs. Transfer to a plate.
Pour the oil into a large, non-stick frying pan ensuring it is no more than two-thirds full, and set over a high heat. The oil is hot enough when a breadcrumb dropped in turns golden in a few seconds. Fry the fishcakes for 2-3 mins on each side until golden and serve with the watercress.
