Mix the flour with the baking powder, sugar, vanilla sugar and the orange peel. Mix with the diced butter to a crumbly mass.
Lightly whisk the egg and add, knead everything quickly to form a smooth dough. Cover and let rest in the refrigerator for about 30 minutes.
Preheat oven to 175 degrees. Line a baking sheet with parchment paper.
Shape the dough into about 8 cm long, pencil-thick strands. Twist two strands each into a cord and place on the baking sheet. Bake the cookies on the middle rack in the oven for about 15 minutes. Let cool on a wire rack.
Sieve the powdered sugar and mix with the orange juice until thick. Dip the pigtails in half. Scatter the chopped pistachio nuts on top. Let the casting solidify.