Put the fish, peppercorns and bay leaf into
a large, shallow pan, then cover with the
milk and stock. Bring to a very gentle simmer,
then poach the fish for 5-8 mins, skin-side
down, until it just starts to flake at the
thickest part. Lift out the fish and set aside.
Meanwhile, heat the butter in a large
saucepan, then soften the leeks for 10 mins
without colouring. Once soft, turn up the
heat a little and add the cumin seeds, frying
until they sizzle and start to smell toasty. Tip
in the potatoes, then add the poaching liquid
and simmer for 20 mins until the potatoes
are tender and starting to fall apart. Just
before serving, flake the fish and stir through.
Spoon into shallow bowls and serve.