Separate the eggs. Whisk egg yolks, sugar and vanilla sugar in a bowl until frothy. Place the bowl over a bain-marie. Slowly add the milk and stir until thick. Place the bowl to one side. Blend the strawberries with a hand blender until pureed, add to mix and allow to cool. Whisk egg white until stiff. Whisk cream until stiff. Add the whipped egg white to the cold strawberry cream, finally gently fold in the whipped cream. Put the mousse into a glass bowl and refrigerate for 3 hours.
To serve, decorate dessert plates with XUXU and place a nugget of mousse on top.