PREPARE THE WORK SURFACE: Line a large baking sheet (approximately 10x15 inches or a similar size) 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.

CRUSH THE CANDY CANES: 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.

MELT THE DARK CHOCOLATE LAYER: Combine the dark chocolate and the optional coconut oil or shortening in a large, heat-proof bowl. Melt the chocolate using the microwave method (30-second intervals, stirring well after each) or the double boiler method until completely smooth.

SPREAD AND SET THE DARK LAYER: 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 approximately 20 to 30 minutes, or until the layer is completely set and firm to the touch.

MELT AND FLAVOR THE WHITE CHOCOLATE: Place the white chocolate into a clean, dry, heat-proof bowl. Melt the white chocolate using shorter bursts (15-second microwave intervals) or over very low heat in a double boiler, as white chocolate is more sensitive to heat. 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.

ASSEMBLE AND TOP THE BARK: 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. 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 to ensure they adhere firmly.

CHILL AND BREAK THE BARK: 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 from the refrigerator, peel away the parchment paper, and place it on a cutting board. 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.