Work with 2 bowls, one for the black chocolate and one for the White Chocolate. Keep in a double boiler/bain marie to melt ⅔ of the chocolate, melt and add the rest to temper the chocolate (see instructions in post) or if you don't care to temper just melt the chocolate simply.
Place the chopped Pistachios into the chocolate molds
Pour the Black Chocolate first half amount into the mold.
Let it cool until hard, this might take a while so keep aside.
Now pour the white molten Chocolate on top to finish it off.
Let it cool again until hard, then take the chocolates carefully out and store them in a cool place.