Alternate pouring the dark and white chocolate on the prepared baking sheet to create a swirled pattern about 1/2 inch in thickness. Sprinkle the chopped peppermint evenly over the melted chocolate. Let the chocolate solidify at room temperature. Once solid cover the chocolate with parchment paper and place the tray in the refrigerator for a few hours or overnight, to harden. Break the bark into pieces with a sharp knife and store in an airtight container in the refrigerator, for up to one week.