Mix the starch flour with a small mass of the milk cooled.
Boil the remaining milk and sugar with the scraped vanilla pulp, as well as the slit stick.
Stir the stirred starch flour into the boiling milk and bubble until the sauce thickens. Remove the vanilla pod. Later stir in the egg yolks, stir in the beaten egg whites.
Stir frequently while it cools, otherwise a skin will form.