The trick to this rather luxurious dish is to make an intensely flavored but light-textured red wine sauce out of a couple of salmon heads, and then use the sauce to surround sautéed salmon fillets. Making the sauce takes some time but most of the work can be done ahead.
Ask the fish seller to cut the gills out of the salmon heads, if you buy heads at the supermarket and they still have their gills, cut the gills out by turning the heads over and using heavy shears to cut the gills out of each side of the heads. Discard the gills and soak the heads for 30 minutes in cold water.
Put the onion, carrot, celery, garlic, thyme, bay leaves, and olive oil in a