Soak the gelatin sheets in cold water for about 10 minutes.
Whip the cream to whipped cream (whip lightly and then place in the refrigerator).
Boil the blueberries for 5 minutes together with sugar and vanilla sugar.
Squeeze the water out of the gelatin sheets and melt them in the blueberries.
Let the mixture cool to room temperature.
Fold the yogurt into the mixture.
Then fold the whipped cream into the mixture.
Distribute the mousse on the cake layers or in glasses and refrigerate for a few hours, preferably overnight.
I added blue pasta color to the mousse to make it blue.
Otherwise it will be light pink.