Prepare a syrup by heating the water, sugar, and grated citron zest until boiling. Allow it to cool, then strain.
Add the citron juice and the torn basil leaves. Leave to infuse for around 30 minutes, then strain again.
Pour the mixture into a shallow container and place it in the freezer. Stir with a fork every 30 minutes for 3–4 hours to achieve a fine, smooth texture.
Serve the sorbet decorated as desired.
