Peel the prawns, leaving the tails intact.
Make 800 ml fish stock from the heads and skins, and season with salt and pepper.
Add the fish sauce and clarify the stock.
Steam the prawns.
Chill the soup bowls in the refrigerator.
Pour 125 ml of the fish stock into a small saucepan and add the gelatine. Allow it to sponge for five minutes, then heat gently until completely dissolved.
Pour this mixture into the remaining stock and stir well.
Put the bowl over a larger bowl of crushed ice to speed up setting.
Pour a little jellied stock into each mould and refrigerate for five minutes to set.
Completely cover the layer of jelly with the slices of tomato.
Add the prawns to each bowl and sprinkle with chives.
Cover with the remaining jelly and refrigerate until set.
Season with freshly ground black pepper and serve with wedges of lemon and oasted French bread, sprinkled with olive oil and salt.
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