Soak gelatine in cold water. Wash the limes in hot water, rub the peel of 1 lime finely. Cut all limes in half. Put 1 half aside for garnishing. Squeeze the fruit, measure out approx. 80 ml juice.
Mix coconut milk, 3-4 tablespoons sugar, lime zest and juice. Squeeze the gelatine well and eyelet it at mild heat aufl Stir 4-5 tbsp coconut milk into the gelatine. Stir this into the remaining coconut milk and chill.
Whip the cream until stiff and allow the vanilla sugar to trickle in. When the coconut milk begins to gel, fold in the cream. Divide the lime-coconut mixture into four glasses (each containing approx. 300 ml) and chill for approx. 4 hours.
Clean, wash and drain the blueberries well. Mix with 2 tablespoons of sugar. Bring half the berries and 5 tbsp. water to the boil while stirring. Stir in the rest of the blueberries and let cool down.
To serve, spread blueberries on the mousse. Cut the lime half into thin slices. Decorate dessert with it.