Cook the potatoes in boiling salted
water for 10-15 mins until tender. Drain
in a colander over the spinach so the
leaves wilt. Return the potatoes to the
pan to steam-dry, then roughly crush
with a fork. Leave to cool.
In a separate pan, poach the haddock
in the milk with the bay leaves and
peppercorns for 4 mins. Turn off the heat
and leave to cook for a few mins more
until the flesh flakes. Remove to a plate
and break into large pieces, discarding
the skin and any bones.
Mix the cooled potato, wilted spinach
and haddock with the egg yolk and 3 tbsp
of the poaching milk. Form into 4
chunky cakes and chill in the fridge,
covered, for at least 30 mins, or
overnight. Mix all the mayonnaise
ingredients together and chill.
Heat the oil in a large pan over a
medium heat. Sprinkle flour over the fish
cakes and fry for about 5-6 mins on each
side until golden and heated through.
Serve with lemon wedges and a dollop
of the horseradish mayo.