Line a large baking sheet (approximately 10x15 inches or similar) with parchment paper or a silicone baking mat. Ensure the lining extends over the sides to make removing the finished bark easier. Set the prepared pan aside.

Place the peppermint candy canes into a heavy-duty zip-top bag. Seal the bag and use a rolling pin or heavy object to carefully smash the candies until they are crushed into a mixture of small and medium-sized pieces. Set the crushed candy aside.

Combine the dark chocolate and the optional coconut oil or shortening in a large, heat-proof bowl. Melt the chocolate either in a microwave (stirring every 30 seconds) or using a double boiler over simmering water until completely smooth.

Pour the melted dark chocolate onto the center of the prepared baking sheet. Use a spatula or offset knife to spread the chocolate evenly into a thin layer (approximately 1/8 to 1/4 inch thick). Transfer the baking sheet to the refrigerator and chill for 20 to 30 minutes, or until the dark chocolate layer is completely set and firm to the touch.

Place the white chocolate into a separate clean, dry, heat-proof bowl. Melt the white chocolate using extreme care—use 15-second intervals in the microwave or melt over very low heat via a double boiler. Once nearly smooth, remove from the heat source and stir in the 1/2 teaspoon of peppermint extract until the mixture is fully incorporated and smooth.

Pour the melted white chocolate over the solidified dark chocolate layer. Quickly use a spatula or offset knife to spread the white chocolate evenly over the dark chocolate, working fast as the cold base will cause the top layer to set quickly.

Immediately and generously sprinkle the reserved crushed candy canes over the top of the wet white chocolate layer. Gently press the peppermint pieces into the white chocolate with the back of a spoon to ensure they adhere firmly.

Return the baking sheet to the refrigerator and chill for at least 1 to 2 hours, or until both layers are completely firm and solid. Remove the bark, peel away the parchment paper, and use your hands to break the chocolate slab into irregular, bite-sized pieces.