Recipe video above. This is a one-pan meal with fish baked on top of a potato gratin in a creamy sauce with a golden crunchy topping. It's a cross between a casserole, gratin and a pie. The idea is that the panko acts like a lid, keeping the fish succulent as it bubbles away in the cream while the gratin soaks up the tasty fish juices.This is a fabulous cosy, rustic oven baked fish recipe that's effortless yet company worthy!