Roll out the puff pastry and cut it into strips. Wind the strips of puff pastry onto metal tubes, from the narrower end to the wider end. Bake at 200°C for about 10 minutes. While still warm, remove from the metal tubes and let cool. Meanwhile, prepare the cream. Pour most of the milk into a pot, add sugar and vanilla sugar. Add the vanilla pudding mix, egg yolks, and flour mixed with a little milk, and cook until the cream starts to thicken. While the cream is still warm but not hot, whisk in the butter and let the cream cool, stirring occasionally. Fill the baked tubes with the cooled cream and dust with powdered sugar.