Fold the flanges around the fish so that it is completely covered. Place the packed fish onto the tray. Beat the egg whites and add salt. Continue beating until the egg white foam is very firm. Spread the egg white foam evenly over the fish with a palette knife so that it is sealed airtight. Draw an eye, head, scales and a tail with the palette knife. Do not wait too long, otherwise the egg white will become soft again. Place the baking tray in the oven and bake for 20 minutes.