Place the 3 quarters of the cod in a large food processor and blitz until smooth. Retain the meatiest quarter of the cod and give it a small dice.
Transfer the puree and diced cod to a large bowl. Add egg yolk, salt and a tablespoon of cornstarch.
Pipe the cod mixture onto a baking sheet in 2 ½" long logs. Transfer the baking sheet to the freezer and freeze for 1 hour.
Place all of the ingredients in a large bowl and stir to combine. Cover and chill until ready to serve.
Working with one stick at a time, roll the fish sticks in the flour/cornstarch mixture, followed by the eggs, followed by the panko.
Working in batches, fry the fish sticks until golden on both sides – about 2-3 minutes per side.