01 - Line a 9x13 inch baking sheet with parchment paper.
02 - Melt the dark chocolate in a heatproof bowl over a pot of simmering water (double boiler) or in short intervals in the microwave, stirring until smooth.
03 - Stir the peppermint extract into the melted dark chocolate until well combined.
04 - Pour the melted dark chocolate onto the prepared baking sheet and spread into an even layer about 1/4 inch thick.
05 - Melt the white chocolate using the same method, being careful not to overheat.
06 - Drop spoonfuls of melted white chocolate randomly over the dark chocolate. Use a skewer or toothpick to swirl the white chocolate into the dark chocolate, creating a marbled effect.
07 - Sprinkle crushed peppermint candies evenly over the top, if using.
08 - Refrigerate for about 45 minutes, or until completely set and firm.
09 - Break the bark into pieces and store in an airtight container at cool room temperature or in the refrigerator.