Put the candy canes in a plastic bag and crush them with a mallet. Mix the melted dark chocolate with the peppermint oil, and spread this mixture evenly into a 12- by 16-inch baking sheet lined with parchment paper. Put the baking sheet in a refrigerator to harden the candy quickly. Once the dark chocolate mixture has hardened, spread the melted white chocolate evenly over the top of the hardened dark chocolate mixture and then quickly sprinkle the crushed candy canes uniformly over the white chocolate. Refrigerate the baking sheet again to quickly harden the candy. Break the candy into pieces and store it in an air tight container in a cool place until you are ready to serve it.