Preheat oven to 400 °F (200 °C).
Beat the egg yolks with the confectioner’s sugar and vanilla sugar until white and creamy.
In a separate bowl, begin to beat the egg whites, add the granulated sugar, and beat to stiff peaks.
Fold the two mixtures together, but not completely.
Sift the flour and carefully fold it in.
Using a piping bag fitted with a round nozzle, pipe ladyfingers onto a baking sheet lined with parchment paper.
Dust with powdered sugar and bake for 5–8 minutes.
Keep the oven open slightly while baking.
