8 ounces good-quality white chocolate
8 ounces bittersweet chocolate
4 tablespoons heavy cream
3/4 teaspoon peppermint extract
6 candy canes, smashed (or 4-5 ounces peppermint candies)
Turn over a large baking sheet. Cover securely with foil and tape in place.
Coarsely chop white chocolate and transfer to a medium stainless steel mixing bowl. Reserve.
Combine bittersweet chocolate, cream and peppermint extract in medium, heavy-bottomed saucepan over low heat and stir until just melted and smooth. Cool for 5 minutes. If the chocolate seizes up, just add a bit more cream and heat until soft again. Using a large offset spatula, spread bittersweet chocolate in even layer. It should be about 9x12. You can also just roll it out with a rolling pin if need be - just plop the chocolate onto the foil-covered baking sheet, cover with a large piece of plastic wrap and roll out. Refrigerate until very cold and firm, about 25 minutes.
Unwrap candy canes or peppermint candies and place in a heavy duty ziploc bag. Smash with a rolling pin or meat tenderizer until pulverized. Reserve.
Bring an inch or two of water to boil in a wide saucepan or saute pan. Turn off heat and set bowl of white chocolate on the hot water. Stir until the chocolate is melted and smooth. Remove from water bath and let cool for 3-5 minutes. Pour onto bittersweet chocolate. Using icing spatula, spread to cover the bittersweet chocolate. Sprinkle candy cane dust and bits all over surface. Chill until set, about 30 minutes.
Lift foil with bark onto work surface; trim edges. Break into medium large shards. Let stand 15 minutes at room temperature before serving.
Can be made 2 weeks ahead. Store refrigerated in an airtight container.