Start by lining up a 15 × 10 inch jelly tray (baking sheet with raised edges) with parchment paper. This will prevent the chocolate crust from sticking to the pan.
Cut the dark and white chocolate into thin pieces to melt better in the next step, and crush your peppermint into small pieces.
Place finely chopped dark chocolate and 1 teaspoon of mint extract in microwave-safe bowl for 30 seconds at a time, stirring between them, until completely smooth.
Pour the melted dark chocolate onto the lined baking sheet and gently spread with a knife or silicone spatula until smooth. If you don't fill the pan, it's okay, everything will eventually break!
Repeat the process with the finely chopped white chocolate, add 1 teaspoon of mint extract, then microwave for 30 seconds at a time, stirring between them, until completely smooth.
Add 2 ounces of crushed candy canes (or peppermint candies) to the white chocolate, then pour over the still hot and melted dark chocolate. Use a knife or spatula to spread it gently, doing your best not to disturb the dark chocolate underneath.
Sprinkle the remaining crushed mint candies over the white chocolate.
Set the pan aside and let it harden at room temperature for several hours or overnight. If you want faster results, you can let it cool for 15 minutes and then put it in the fridge for at least 1 hour or until it's completely hardened.
Once it's completely cool and hard, break it into medium-sized pieces with your hands or with a sharp knife.
Store in an airtight container until ready to use.
Note: You must make sure to prepare the white chocolate immediately after pouring the melted dark chocolate into the pan, as the dark chocolate has not yet melted and heated when the white chocolate is added for better mixing.