Line a baking sheet with parchment paper, making sure it covers the entire surface.
In a heatproof bowl, melt the chopped white chocolate using a double boiler or microwave in 30-second intervals until smooth.
Once melted, remove the chocolate from heat and stir in ¾ cup of chopped pistachios and all of the dried cranberries until well combined.
Immediately pour the chocolate mixture onto the prepared baking sheet and spread it out evenly with a spatula, about ½ inch thick.
Sprinkle the remaining pistachios and sea salt (if using) over the top of the bark, pressing them gently into the chocolate.
Allow the bark to cool at room temperature for about 15 minutes, then refrigerate for 1 hour or until completely set.
Once set, remove the bark from the baking sheet and break it into pieces or cut it into squares using a knife.
For a festive twist, consider adding a sprinkle of crushed peppermint candies or colorful sprinkles on top before refrigerating.
Store any leftovers in an airtight container in a cool, dry place for up to two weeks.