Drain the juice from the can of salmon into a saucepan. Break the fish into flakes putting the bones and skin into the saucepan with the juice but setting the flakes to one side. Peel the prawns. Put the heads and shells into the saucepan and set the prawns to one side with the salmon flakes. Add the vegetable stock, onion and bay leaf to the saucepan. Bring to the boil. Reduce heat, cover and simmer for 45 minutes. Remove the consomm� from the heat and strain it into a jug through a sieve which has been lined with damp muslin. Wash out the pan and return the consomme to the saucepan, once again passing it through a sieve, lined with clean, damp piece of muslin. Whisk the egg whites until they form stiff peaks. Place the consomme over moderate heat and bring to the boil. Whisking gently, add the egg whites, a spoon at a time into the stock. When the mixture boils, simmer gently for 10 minutes, without breaking the crust of egg white which will form over the top. Allow to stand for 5 minutes before straining it for a final time through a sieve lined with dampened muslin. Reheat the soup before serving in bowls along with the flakes of salmon, shelled prawns, carrot flowers and sherry, if used. Serves 2. Approx. 290 kcals per serving