In a medium saucepan, combine cream, water, syrup and cocoa powder. Bring to a simmer and stir until cocoa powder dissolves.

Remove from heat and stir in chocolate and vanilla extracts. Pour mixture into an 8 inch square pan.

Freeze until almost solid, about 3 hours.

To serve, break frozen mixture, place in a blender or food processor and blend until softened and slushy. Transfer to glasses and serve.