Prepare your workspace by lining a baking sheet with parchment paper, making sure the paper extends slightly beyond the edges for easy removal later.
Melt the dark chocolate in a microwave-safe bowl at 50% power, stirring every 30 seconds until smooth and completely melted. Be patient—chocolate burns easily!
Add 1/4 teaspoon of peppermint extract to the dark chocolate if using, and stir well to incorporate the flavor throughout.
Pour the melted dark chocolate onto the prepared baking sheet and use a spatula to spread it into an even layer about 1/4 inch thick. Don’t worry about making perfect edges.
Let the dark chocolate layer set until the surface is matte but still slightly tacky, about 15-20 minutes at room temperature (5 minutes in the refrigerator).
Melt the white chocolate using the same method as the dark chocolate, being even more careful as white chocolate scorches more easily.
Add the remaining 1/4 teaspoon peppermint extract to the white chocolate if using, stirring well to combine.
Pour the white chocolate over the partially set dark chocolate and gently spread it into an even layer, being careful not to mix the two chocolates together.
Immediately sprinkle the crushed candy canes over the white chocolate layer while it’s still wet, pressing larger pieces gently to ensure they stick.
Finish with a light sprinkle of flaky sea salt across the entire surface, using your fingers to control the distribution.
Allow the bark to set completely, either at room temperature for about 2 hours or in the refrigerator for 30 minutes.
Break or cut the bark into irregular pieces using your hands or a sharp knife. For cleaner cuts, use a chef’s knife warmed under hot water and dried.