Wash the fish and pat dry with a paper kitchen towel, then salt both sides.

Dust each fish slice in flour on both sides. Coat with egg and then breadcrumbs, making sure each fish slice is evenly coated.

Fry the fish slices in oil in batches until each side is golden brown on both sides.

To make the pickling liquid, bring 2 litres of water to the boil, then add the salt, sugar and vinegar and stir till dissolved. It needs a sweet and sour taste, but adjust salt/ sugar/ vinegar to achieve a taste you like. Then add the peppercorns and yellow mustard seeds

Layer the fish in a large container, then add a layer of onions. Then alternate layers of fish and onions until all gone.

Ladle the pickling liquid over the fish gently making sure you don’t disturb the the fish, until all the fish is covered.

Cover the container and put it in the fridge for at least 3 days.