In a large microwave-safe dish, heat dark chocolate on 50% power for two minutes.  Chocolate should be about 80% melted; stir to finish melting. (If not 80% melted, continue cooking in 30-second intervals at 50% power until it is.) Stir in 1 tbsp of finely crushed candy cane to melt a bit, then spread on a parchment-lined baking pan to make a rectangle of about 10x7".  Transfer to freezer for 10 minutes.

Wash and dry the bowl completely.  Add white chocolate to the clean bowl and repeat the same melting process.  Let melted white chocolate stand at room temperature for about 5 minutes to cool, then give it a stir and pour evenly over top of cold dark chocolate, quickly spreading it to the edges using an offset spatula (or a pie lifter). You don't want the chocolate to be too cool or it will be too thick to easily spread thinly, and working it too much with the spatula will start to melt in the dark chocolate. It's ok if it happens. It will remain delicious. Sprinkle the bark with crushed candy canes and let stand at room temperature until set, about 2 hours, or overnight.

Use the parchment to lift the bark and break it into asymmetrical pieces. Store between layers of parchment or waxed paper in an airtight container for up to two weeks (or maybe longer, if it lasts!).