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, pressing out as much air as possible. Using a rolling pin, a meat tenderizer, or the bottom of a heavy pan, carefully smash the candies until they are crushed into a mixture of small and medium-sized pieces. Set the crushed candy aside in a small bowl.

Combine the dark chocolate and the optional coconut oil or shortening in a large, heat-proof bowl. Melt the chocolate using a microwave (heating in 30-second intervals and stirring) or a double boiler over simmering water until smooth and only a few tiny lumps remain. Stir vigorously until those last lumps dissolve from the residual heat.

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, covering the entire surface or creating a large rectangle shape.

Transfer the baking sheet to the refrigerator and chill the dark chocolate for approximately 20 to 30 minutes, or until the layer is completely set and firm to the touch. This step is crucial before adding the white chocolate layer.

Place the white chocolate into a clean, dry, heat-proof bowl. Melt the white chocolate using the microwave in shorter 15-second bursts or a double boiler over very low heat, stirring frequently. Once the white chocolate is nearly smooth, remove it 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 spread the white chocolate evenly over the dark chocolate using a spatula or offset knife. Work fast, as the cold dark chocolate will cause the white chocolate 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 or your fingertips 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 of the peppermint bark are completely firm and solid. The chocolate must be rigid before breaking.

Remove the bark from the refrigerator. Lift the entire slab of bark off the baking sheet using the parchment paper lining and place it on a cutting board. Peel the parchment paper away from the bottom. Use a large, sharp knife to cut the bark into squares, or simply use your hands to break the chocolate slab into irregular, bite-sized pieces.