Prepare mass number 1. In a mixing bowl add the soft butter, egg yolks, lemon zest, vanilla, all purpose flour and Cornstarch. Mix it all well!
Prepare mass number 2. In another bowl beat the egg whites with the sugar stiff.
Preheat your oven to 350° Fahrenheit/ 180° Celsius.
Add ⅓ of the stiff egg whites (mass nr1.) to the butter-flour mixture (mass nr2) and fold it carefully in so that the airiness remains. Continue to add in the rest of the stiff snow whites and carefully fold it in so that all ingredients are well incorporated.
Butter your molds and dust them with flour. If you use Silicon molds as I did, you won't need to grease them.
Bake your mini Gugelhupf for about 35 minutes at 350° Fahrenheit/ 180° Celsius or until the pastry is properly baked and not raw.