For the lettuce granita
Blend the lettuce with 500g of water and pass through a fine mesh to obtain lettuce juice. Set aside.
Hydrate the gelatin sheets in cold water and set them aside.
Add 150g of sugar to 200ml of water in a pan and make a syrup, heating until it reaches 117°C.
Use a little syrup to dissolve the hydrated and squeezed gelatin sheets.
Mix the remaining syrup and the dissolved gelatin with the lettuce juice.
Put in a container and leave to freeze for at least 12 hours.