Tip the sugar into a bowl, sift in the
cocoa and stir. Bring 600ml water to the
boil in a medium saucepan. Whisk in the
sugar and cocoa and return to a gentle
simmer. Simmer, uncovered, for 5 mins,
whisking occasionally. Remove from the
heat and stir in the chocolate and vanilla
until the chocolate has melted.
Cool the mixture, then put in the fridge
for several hrs or overnight until well
chilled. Make the sorbet in an ice-cream
machine or pour into a rigid plastic
container, preferably bowl shaped, and
freeze until frozen 3cm from the edges.
Whisk to break down the ice crystals,
then freeze again for 1 hr more. Whisk
and freeze again one more time, then
leave until completely frozen.
Before serving, transfer to the fridge
for 30 mins to make scooping easier.