Peel the rhubarb, cut into 1 cm thick slices. Pour the powdered sugar into the pan and heat over low heat until it dissolves slightly. Pour in wine, add rhubarb. Shake the pan to mix the rhubarb with the wine and sugar.
Add vanilla sugar and cook for 6-8 minutes. Transfer the rhubarb with a slotted spoon to a deep serving plate, wide glass or bowl. Boil the remaining liquid for 2 minutes.
Pour the resulting sauce over the rhubarb. Garnish with mint greens when serving.