Combine butter and sugar in a large bowl, using stand mixer or hand mixer. Add baking powder, flour, roughly chopped hazelnuts (or almonds) and chocolate. Mix briefly and add a pinch of sea salt.
divide the dough
Divide the dough into two parts and shape each in a cylinder about 4 cm / 1.5 inch in diameter. Tightly wrap each cylinder in cling film.
Refrigerate for 1 hour or freeze for 15 minutes. Meanwhile, preheat the oven to 180°C / 355°F.
Slice the chilled cookie dough into 1,5cm / 0.5 inch thick slices. Place them in line on a baking tray, lined with parchment paper. Bake for 10 - 12 minutes.TipYour cookies should come out of the oven soft, but once you let them cool they will change consistency.