Drain the oil from the salmon then remove and discard any skin and bones. Put into a bowl and mash, season and add the lemon juice, dill, cayenne and nutmeg.
Add the mashed potatoes, chopped hardboiled eggs, capers and parsley. Mix everything together until thoroughly blended.
Divide the mixture into 6 and shape into individual round cakes, coating each with seasoned flour.
Heat the oil in a frying pan and shallow fry the cakes for a few minutes on each side until they are a nice golden colour. Drain on kitchen paper.
Serve garnished with sprigs of watercress and segments of lemon.