Break the cookies into small pieces in a large bowl.
Add pistachios to the bowl with the cookies.
In a saucepan over low heat, melt the butter, dark chocolate, and condensed milk, stirring until smooth.
Pour the chocolate mixture over the cookies and pistachios. Stir to combine.
Lay out a sheet of cling film. Spoon the mixture onto it and shape into a log or salami form, wrapping tightly.
Place in the freezer for 2 hours to set.
Unwrap and sprinkle with powdered sugar for decoration before serving.