The dish of white fish, typically cod or haddock, fried in a thin coat of flour, was a favourite particularly among Sephardic Jews, who fried it on Friday nights to prepare for the Sabbath, as the Mosaic laws prohibited cooking. Allegedly, the batter preserved the fish so it could be eaten cold, and without sacrificing too much flavour, the following day. [this happened about 1496]

https://www.atlasobscura.com/articles/who-invented-fish-and-chips