Line a baking sheet with parchment paper. Set aside.
Fill a double boiler with 1 inch of water and place it over medium-high heat until simmering. Reduce the heat to medium and add half of the white chocolate to the top pot of the double boiler. Heat until melted, and only a few lumps remain. Remove from the heat and stir in the remaining chocolate until the residual heat has melted it all. (If needed, return to the heat for 30-60 seconds.)
Fold the whole pistachios and dried cranberries into the melted chocolate. Pour onto the prepared baking sheet and spread evenly to your desired thickness. Sprinkle the chopped pistachios and dried cranberries over the chocolate.
Chill in the fridge for at least 30 minutes or until completely hardened. Cut or break into pieces before serving. (see note)
Notes
If you don't have a double boiler available, you can use a medium saucepan and a glass or metal mixing bowl. The bowl needs to cover the entire top of the saucepan, but not touch the water underneath. Be careful while you cook, as the steam will heat the bowl.
If you prefer to cut the bark into pieces, it will be easier if it’s not fresh from the fridge. Let the bark come to room temperature or cut it before it hardens completely.