which is what I usually do with fish. There's 4 fillets of white fish although not entirely sure what kind as my dad bought them last weekend, froze them and then decided he didn't want them so brought them to me this morning!
Mix together grated cheese, big dollop of mustard and enough creme fraiche/yoghurt/cream to bind it into a paste the thickness of marzipan. Squidge on top of fish and bake in the oven until the fish is no longer translucent when you try to flake it. The sauce goes all runny and it is gorgeous! Good with mash or baked potato and veg or salad.