Boil the water with the sugar and the grapefruit zest.
Squeeze the grapefruits to obtain 40cl of juice.
Strain the juice and add it to the syrup with the finely chopped basil leaves.
When the mixture is cold, process in a sorbet/ice cream maker.
Peel the pineapple and chop into large chunks.
Heat the butter and add the honey.
When it has taken on a caramel colour, add the pineapple chunks and continue cooking for a few minutes with the spices.
Finish cooking in the oven at 180 degrees in the frying pan.
Leave to cool before serving with the sorbet.
Decorate with the basil leaves.