Mix the butter, sugar and eggs into a mousse. Add the remaining ingredients and knead. All together should be quite fast and the dough should not warm up too much (even through your hands). Shape the dough into 3 cm thick rolls and let them cool down (one hour is enough, if it will be 48 hours, it won’t hurt). Then cut slices 1 cm wide with a very sharp kitchen knife. If necessary, reshape a little bit, bake on aluminum foil or baking foil at 175 degrees for about 10 min.
For the fake butter, mix egg yolks and sifted powdered sugar until nice and fluffy. Turn the cooled cookies on the other side, spread the “butter” not too thinly on the underside, sprinkle with the pistachios and dry.