Line a baking sheet with parchment paper; set aside.
Place the dark chocolate in a medium heatproof bowl and set it over a small saucepan of barely simmering water over low heat. Melt the chocolate, stirring occasionally, until completely smooth. (You could also microwave on 50% power in 30-second increments, stirring after each, until completely melted.) Using an offset spatula, spread the melted chocolate in an even layer on the prepared cookie sheet. (The melted chocolate doesn't need to cover the entire pan - mine typically covers an area of about a 9x13-inch rectangle.) Place the cookie sheet in the refrigerator while you prepare the white chocolate.
Place the white chocolate in a clean medium heatproof bowl and set it over a small saucepan of barely simmering water over low heat. Melt the chocolate, stirring occasionally, until completely smooth. (Again, you could also microwave on 50% power in 30-second increments, stirring after each, until completely melted.) Remove the cookie sheet from the refrigerator and, using an offset spatula, spread the melted white chocolate in an even layer on top of the dark chocolate layer. Immediately sprinkle the crushed candy canes on top of the melted white chocolate and gently press into the chocolate to adhere. Refrigerate until complete hard and set, at least 30 minutes. Store the bark in an airtight container in the refrigerator for up to 1 month.
Using a large sharp knife, break into pieces and enjoy!