In a large plastic bag, beat the vanilla biscuits into small pieces using a rolling pin.
Coarsely chop the pistachios.
Heat the heavy cream in a saucepan or microwave so that it comes to a simmer (not a boil). Place the chocolate chips in a large bowl and pour the hot cream over the chocolate chips.
Cut the butter into small cubes and place it into the bowl.
Wait a few minutes and begin to stir the chocolate. You may need to reheat the chocolate in the microwave a few more times. If so, heat in 20 second intervals. You don't want to overheat the chocolate.
Once the chocolate is a smooth silky consistency, add the crushed biscuits and chopped pistachios. Stir to combine.
Place a large piece of plastic wrap onto a flat surface and pour the chocolate mixture on top.
Roll the plastic tightly around the chocolate mixture so that it resembles a stick of salami. You can wrap a second piece of plastic wrap over the chocolate salami if you want to make it more secure. Finish off by tying both of the ends.
Refrigerate for at least 4 hours. Once the time has passed, remove the plastic wrap and coat the chocolate salami in powder sugar.