For the wild berry yogurt tiramisu, whip the whipped cream with the vanilla sugar and the cream stiffener until stiff.
Sweeten the yogurt with sugar to taste, then fold in the whipped cream. Place 2 spoonfuls of the whipped yogurt cream in a baking dish, then place a layer of sponge cake on top.
Run a little cocoa over the top, then another layer of cream. Sprinkle the fruit on top, then another layer of sponge cake, cocoa and cream.
On top you can then sprinkle some more fruit or sprinkle with cocoa or chocolate shavings.