Mix the mascarpone with the yogurt until creamy. Beat the cream with the cream stiffener until stiff. Mix the whipped cream with the yoghurt - mascarpone - cream and the vanilla sugar to a homogeneous mass and pour over the frozen fruits. As the top layer, sprinkle the brown sugar evenly over it very thickly. There must be no more cream to be seen!
It is best to put it in the refrigerator until the next day.