Break the chocolate into small pieces and put in bowl with butter.
Melt in a water bath.
Mix until smooth and shine.
Beat eggs with sugar until white.
Add the chocolate and mix gently.
In the same bowl sift flour with baking powder and mix one more time.
Now you can add the peeled pistachios.
Pour batter into a greased and floured form and smooth.
Bake 30 minutes at 190 degrees, then remove from oven and let cool down.
Cut into squares and serve.