Pour the water and sugar in a pan, bring to the boil and divide in half. Add the lemongrass, chilli, star anise and vanilla in one half and bring to the boil.
Peel the pineapple, cut in half, and on a Japanese mandolin slice ribbons with one half of the pineapple. Place in a bowl and pour over the spiced syrup. Cover and leave in the fridge for 2 hours.
Chop the other half into chunks and whizz in a blender. Add the other half of the syrup and churn in an ice cream machine.
To serve arrange the sliced pineapple in a bowl, add a spoon of sorbet and top with the coconut. Spoon on dollops of jelly.
For the lemongrass jelly:
Bring the water and sugar to the boil. Add the zest, juice and lemongrass and infuse for 2 hours.
Pass through a sieve, gently warm, add the gelatin, pass through a sieve again and set in the fridge.
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