The colors of the holiday season are built right into this festive bark. Feel free to experiment with other fruits and nuts.
1. Roughly chop the pistachios and cranberries. Chop the chocolates, keeping them separate. Place each in a separate medium heatproof bowl. Arrange bowl with dark chocolate over saucepan of simmering water (do not let bottom of bowl touch the water) and heat dark chocolate until melted, stirring often. Remove bowl and repeat with bowl of white chocolate.
2. Pour melted dark chocolate onto a parchment-lined baking sheet. Smooth into a thin, even layer (it will not cover the entire pan). Dollop white chocolate onto dark chocolate. With the tip of a knife, swirl together dark and white chocolates.
3. Sprinkle evenly with chopped pistachios and cranberries. Refrigerate bark until set, about 1 hour. Break into pieces. Store in a sealed container or plastic bag in the refrigerator.