Combine butter, sugar, vanilla sugar, and salt. Beat for 2-3 min until creamy. Add eggs and beat for 1-2 min until frothy.
In a separate bowl, mix flour, cornstarch, and baking powder. Gradually stir the dry ingredients into the wet mixture. Add condensed milk and stir until combined.
Pour dough into a greased 30 cm (12 inch) round cake pan. Bake in a preheated oven at 160°C (320°F) for 20-25 min.
Alternatively, divide dough among 15 silicone tartlet molds (12 cm diameter, 2 cm height) and bake in a preheated oven at 160°C (320°F) for roughly 15-18 min until set.