Line a baking sheet with parchment paper. This will prevent the chocolate from sticking and make it easier to remove once it's set.
Using a double boiler, melt the dark chocolate over simmering water. If you don't have a double boiler, you can use a microwave-safe bowl. Heat the chocolate in 30-second intervals, stirring in between until fully melted.
Once melted, add 1/4 teaspoon of peppermint extract to the dark chocolate and stir well.
Pour the melted dark chocolate onto the prepared baking sheet. Use a spatula to spread it into an even layer, about 1/4 inch thick.
Place the baking sheet in the refrigerator for about 20 minutes to allow the dark chocolate to set.
While the dark chocolate is setting, melt the white chocolate using the same method as the dark chocolate.
Add the remaining 1/4 teaspoon of peppermint extract to the white chocolate and stir well.
Once the dark chocolate has set, remove the baking sheet from the refrigerator.
Carefully pour the melted white chocolate over the dark chocolate layer, spreading it evenly with a spatula.
Immediately sprinkle the crushed candy canes or peppermint candies over the white chocolate layer. Press them down gently with the spatula to ensure they stick.
Place the baking sheet back in the refrigerator and let the peppermint bark set for at least 1 hour.
Once the peppermint bark is fully set, remove it from the refrigerator.
Lift the parchment paper to remove the bark from the baking sheet, and then break it into pieces of your desired size.
Your peppermint bark is now ready to enjoy! Store any leftovers in an airtight container at room temperature for up to two weeks.