Mojito Nitro Cocktail (Liquid Nitrogen Sorbet)

Makes 300 ml.

1. Slice the ends off 4 limes, then cut a small coin from the bottom so the limes can stand up.
2. With a sharp knife, hollow out the fruit flesh from the limes, reserving the flesh and juices. Put the hollowed-out limes in the freezer.
3. Cut the remaining limes in half and squeeze the juice.
4. Boil the sugar in the water and set aside to cool.
5. Blanch the mint in boiling water for 5 seconds, then chill immediately in ice water.
6. Finely chop the blanched mint and purée it with the sugar water to make a mint syrup; strain completely.
7. Combine 100 ml rum, 50 ml lime juice and 150 ml mint syrup. Shake in a cocktail shaker and pour into a double-walled bowl.
8. Carefully pour liquid nitrogen into a vented stainless steel thermos (never use a sealed thermos or ordinary measuring cup).
9. Slowly pour the liquid nitrogen into the mojito mixture, whisking gently to distribute the cold evenly, until you have a sorbet.
10. Scoop the sorbet immediately into the frozen hollowed-out limes and garnish with a mint sprig. Serve immediately with a small spoon.

Serving suggestions: As a pre-dinner cocktail; as a dessert amuse-bouche; or as part of a dessert plated with yoghurt and red or exotic fruit.