Paupiette of Rainbow Trout with Leeks on Caviar Sauce

This recipe is for a first course, but it is also good as a light meal for four people. I know that caviar is expensive, but it really does go rather well with the trout; if you cannot stretch to caviar, then try adding leaves of fresh thyme instead. They are obviously not quite the same, but are definitely a lot cheaper and almost as good. Use the youngest, thinnest leeks possible (pencil thickness if possible) as they have a far superior flavour and are that much more tender.