Line a baking sheet with parchment paper and set aside.
Melt the white chocolate over a double boiler (or in 30-second intervals in the microwave on 50% power, stirring after each). Once the chocolate is melted, remove from the heat and let sit for a few minutes to cool slightly, stirring occasionally. Add the pistachios and cranberries and stir to combine.
Spread the chocolate mixture onto the prepared pan in an even layer (depending on the size of the pan and how thick you'd like your bark, you may not need the entire surface of the pan).
Refrigerate for at least 30 minutes, or until set.
Using a sharp knife, cut the bark into pieces. Store in an airtight container in the refrigerator.