Pop the dates in a small bowl and cover with one cup (250ml) of boiling water. Leave to stand for 20 minutes.
The coconut cream should have separated overnight. Carefully scoop the thick cream into a large mixing bowl. (You can discard the water or keep it for another dish.) Beat the cream for a minute or two until it forms stiff peaks.
Discard 3-4 tablespoons of liquid from the soaking dates. Use a stick blender or food processor to whizz the dates into a smooth purée. Add the date purée to the cream. Sift in the cocoa powder and add the vanilla extract.
Gently stir the ingredients together until combined and smooth. Spoon the mousse into ramekins or glasses and pop in the fridge until chilled and set.