Cut the vanilla pod in half lengthways and scrape the
seeds into a small saucepan. Add the sugar and water and place over a high heat, stirring until the sugar dissolves. Bring to a boil without stirring for 1
minute. Cool in the fridge until the syrup is completely cold.
Stir together the syrup, grapefruit juice, lemon zest
and juice and the chopped basil. Pour into a shallow glass or nonreactive tray and place in the freezer. Every 30 minutes, take the tray out of the freezer and stir the
granita with a fork to break it up. Keep doing this until the granita is frozen throughout. This will take
about 3 hours.
To serve, scoop the granita into glasses. Decorate with a
sprig of fresh basil and serve with biscotti biscuits.