It started out as a way to sell the cheeks and off-cuts of cod that fishmongers couldn't sell whole, not as a dish built from prime fillets.
Bite-sized chunks of white fish are battered and deep-fried until crackling-crisp, then served in a paper tray with a garlicky sauce for dipping. Fish stalls at markets across Noord-Holland, especially around Amsterdam and Volendam, sell it as an eat-while-you-walk snack.