Combine the water, hazelnuts, cacao powder, dates, and vanilla in a high-speed blender, and blend until smooth. If you taste it now, keep in mind that the flavor will be diluted when you add the ice.
Add in the ice cubes and blend again, until a slushy texture is achieved. If you use less ice, the flavor will be more concentrated, adn if you add more, the flavor will be diluted, so keep that in mind.
Serve right away for the best taste and texture.
Nutrition information is for the whole batch, and is just an estimate not a guarantee. Feel free to split this into two servings for a lower calorie dessert.