Mix the softened butter with the sugar, vanilla sugar and salt in a bowl. Beat the mixture to obtain a creamy paste. Add the eggs one by one, mixing well. In a second bowl, mix the flour, ground hazelnuts, Gavottes and baking powder. Gradually add this mixture to the previous mixture. Add the chocolate chips. Roll the dough into small sausage-shaped rolls then refrigerate. Preheat the oven to 210°C (th.7). Cut the rolls into slices 5 mm thick. Place them on a baking tray. Bake for around 10 minutes at 180°C. Remove from the oven and transfer the cookies to a rack to cool.