Peel 4 bananas and mash with a fork. Sprinkle with lemon juice and mix very thoroughly with yogurt, vanilla sugar and powdered sugar.
Mix the mascarpone and gently fold in the stiffly whipped cream.
Peel the 5th banana and cut into fine slices.
Also gently fold in. Chill everything for 1 hour and then serve with chocolate sauce or melted chocolate.