Creamy Fish Gratin

This changes the whole concept of fish pie from a hearty meal that needs an hour or two to prepare, to a light and creamy dish that takes less than half an hour. I got the idea from a Russian cookbook I worked on in which there were a couple of recipes that used smetana (similar to creme fraiche) to cover a whole fish before baking. The smetana sealed the fish in the same way as the Spanish use salt. So I used the same method to poach fish pieces topped with cheese and breadcrumbs, and it works perfectly. You don't need to precook the fish, you don't need to make a bechemal sauce and you don't need to boil and mash potatoes.