Line a 9x13-inch baking sheet with parchment paper and set aside.
Melt the dark chocolate in a microwave-safe bowl in 30-second intervals, stirring between each, until completely smooth.
Pour the melted dark chocolate onto the prepared baking sheet and spread evenly with a spatula. Refrigerate for 15-20 minutes until firm.
Melt the white chocolate using the same method, then stir in the peppermint extract.
Pour the white chocolate over the dark chocolate layer and spread evenly.
Immediately sprinkle the crushed candy canes over the top, pressing down gently so they stick.
Refrigerate for 30 minutes until completely set, then break into irregular pieces and store in an airtight container.