Peel and finely dice the shallots.
Heat a saucepan, add the butter and allow to melt. Add the shallots to the pan and cook until soft. Add the peas, water and half of the lemon balm. Cook for 10 minutes and then add the cream. Bring to the boil and then transfer to a food processor. Blend until smoooth and then pass the soup through a sieve. Allow to cool.
Finely chop the rest of the lemon balm, and add to the cold soup.
Peel the prawns and remove the digestive tract. Cook the prawns in olive oil and then season with salt and piment d'Espelette.
Serve the prawns with the pea soup.
«Feel free to use mint if you cannot get hold of lemon balm.»