Preheat the over to 160° C w/ fan.
Line 2 baking trays w/ baking parchment.
Prepare the lemon zest.
Mix sugar, vanilla sugar & salt, add the soft butter & mix w/ your handheld electric mixer.
Add egg yolks & lemon zest & mix.
Mix flour & baking powder; add the sugar-butter-egg mess & mix.
Mix milk & vanilla essence, add to the mess & mix.
Knead the batter until all is combined.
Take a tespoon & make small heaps of batter (about 40).
Arrange the heaps (4 x 5) on the baking trays.
Flatten the heaps & take a fork to add some more structure.
Bake in the preheated oven for about 12 - 14 min.
Let the cookies cool down completely & store them in an airtight container.
OPTIONAL: melt some dark chocolate & add to the cookies.