Step 1Heat the sugar, water and vanilla bean in a saucepan over medium heat, stirring occasionally to dissolve the sugar. Bring the mixture to a boil, then reduce the heat and simmer 10 minutes.
Step 2Remove the saucepan from the heat and whisk in the chocolate and cocoa, stirring until the chocolate is completely melted. Remove the vanilla bean. Pour the mixture into a shallow baking dish and freeze until solid, several hours or overnight.
Step 3Whip the cream or creme fraiche to soft peaks. Spoon or scoop the granita into dessert or parfait glasses and top with whipped cream or creme fraiche.