Boil the potatoes. Drain and mash with the butter.
Mix the hard-boiled eggs, spring onion, lemon rind
and juice, parsley, tuna, capers and 25ml/1 tbsp of
the beaten egg into the cooled potato. Season to
taste, cover and chill.
Mix all the sauce ingredients together. Chill in the
fridge.
Roll the fishcake mixture into about 24 balls. Dip
these into the egg and then roll gently in the
breadcrumbs until evenly coated. Transfer to a
plate.
Heat 90ml/6 tbsp of the oil in a frying pan and fry
the balls over a moderate heat, in batches, for
about 4 minutes, turning two or three times until
browned all over. Drain on kitchen paper and keep
warm in the oven while frying the remainder. Serve
with the tartar sauce and a salad.