For the chocolate cookies, mix flour with the baking powder and cocoa, chop cool butter. Knead the flour, butter, sugar and egg into a dough. Form small 1.5 cm balls and cut them crosswise with a knife.
Bake at 180 °C for about 15 minutes. When the chocolate cookies have cooled down, pour the melted chocolate into the resulting grooves and sprinkle with the chopped pistachios.