1. Melt the dark chocolate on the stove-top in a double boiler or in the microwave at 50% power, about 4 minutes, stirring frequently.
2. Line a baking sheet with parchment paper. Pour the melted chocolate onto the sheet and spread it out with a spatula. The chocolate does not have to be perfectly level; the change in thickness is a nice touch.
3. Allow the dark chocolate to set until firm, about 45 minutes. Melt the white chocolate and spread it on top of the dark chocolate.
4. Sprinkle the white chocolate with the crushed peppermints and allow to harden in a cool, dry place, about 45 minutes. Break the bark into small pieces and store in an airtight container in the refrigerator for up to a week.