Line a half sheet pan with aluminum foil, making sure it's smooth.
Place the white chocolate in a microwave-safe bowl. Heat in the microwave at half-power in 30-second increments until the chocolate melts when stirred. (Alternatively, melt the chocolate in a double boiler.)
Spread the melted chocolate in an even layer on the prepared pan. About 1/4-inch thick is ideal.
Sprinkle the cranberries and pistachios over the top of the chocolate, and press down lightly.
Allow the chocolate to set completely in the refrigerator for an hour or so before breaking or cutting into pieces.
Notes
*These amounts are a guideline. You can easily adjust up or down depending on your preferences.
The yield will vary depending on how you break or cut the bark.
Store in an airtight container at room temperature for several days.