In a big bowl, combine the flour, salt, sugar, vanilla sugar, baking powder. Add the grated butter, orange zest and mix with fingers or spoon until it forms crumbs.
Add the egg, mix until the dough is even (don't knead it). Form a ball. Rest in the fridge for about 1 hour.
Remove the dough from the fridge and let sit about 15 minutes at room temperature.
Preheat the oven to 180 C temp. Line a baking sheet with baking parchment.
Cut the dough into 2 pieces. Form 2 oblong rolls. Cut into 20 pieces each and roll them into small balls.
Place on the baking sheet. Using fingers, press each one down gently and form about 3 1/2 cm diameter.
Brush the cookies with the egg white and sprinkle the almond flakes over the top.
Bake about 10 minutes. Leave to cool and store in a covered container.