In a large bowl, whisk together the flour, ground hazelnuts, sugar, vanillin sugar, and salt. Add the soft butter and egg to the dry ingredients. Mix everything together until it forms a smooth dough.
Wrap the dough in plastic wrap and let it rest in the refrigerator for 1 hour.
Preheat your oven to 180°C (350°F) and line a baking sheet with parchment paper.
Remove the chilled dough from the refrigerator. Take small portions of dough (about a tablespoon each) and roll them into small logs. Gently curve each log into a crescent moon shape. Place the crescents on the prepared baking sheet, leaving some space between them.
Bake for 10-15 minutes, or until the edges are just slightly golden.
Let them cool completely on a wire rack.
Once the crescents are cool, melt the dark chocolate with the vegetable oil in a double boiler.
Dip each end of the crescents in the melted chocolate or drizzle it over them.
Place on parchment paper and let the chocolate set.
