The first four ingredients are for the raspberry puree.
Put the water and sugar in a pan, bring to the boil and leave to cool.
Put the raspberries in a food processor and add the sugar syrup and lemon juice. Blitz to a smooth puree and then pass through a sieve.
Put the second lot of water and sugar in a saucepan and bring to the boil.
Add the cocoa powder and continue to cook over a low heat for 2-3 minutes.3 Pass the mixture through a fine sieve into a bowl containing the chopped chocolate.
Mix until the chocolate has melted and it is completely smooth. Cool rapidly over an ice bain-marie (water bath) and then mix in the raspberry puree.
Churn the mixture in an ice cream machine following the manufacturer's instructions.
If you don't have an ice cream machine, churn by hand.
Mix in a bowl and freeze for about 90 minutes until it starts to freeze around the edges. Stir well, then repeat the process twice more until the mix is smooth and frozen.