Charlie, we made 'salmon en croute' lots at a catering job I had; the oh, so elegant French chef made his w/puff pastry; we would spread out the sheet of pastry, lay down a layer of a very thick veloute sauce (just like a bechemal only made with stock instead of milk, and he flavored his w/tarragon), then a layer of very well drained cooked spinach, and and then chopped cooked mushrooms. Over that we laid the salmon fillet, and then brought up the edges of the pastry over the top of the fish and sealed it. I'll never forget the day when he gave me the honor of making all the little pastry decorations to go on top! The extra veloute was warmed and served over the fish after cooking.