Whisk together the all-purpose flour, cake flour, and baking powder. Add the softened butter and mix until combined.
Add the sugar and vanilla sugar, using a wooden spoon or your hands to mix. Add the egg and mix until just combined.
Wrap the dough in plastic wrap and let it rest in the refrigerator overnight or for at least 8 hours.
Preheat the oven to 350F. Remove small pieces from the dough and roll each piece into a small ball, approximately 1 inch in diameter. Place each ball on a baking sheet and lightly press down with your thumb to slightly flatten each one.
Brush the cookies with egg white and sprinkle pearl sugar on top of each one. Bake at 350F for 16-18 minutes or until the cookies become lightly golden in color.