Grease the bottom and sides of a 9×13-inch baking sheet or pan with coconut oil. Line the pan with parchment paper, pressing the paper against the coconut oil to adhere to the pan.
Place the bittersweet chocolate in a heatproof container set over gently simmering water in a saucepan. Heat, stirring often, until melted. Add in peppermint extract and salt.
Carefully spoon the hot melted chocolate onto the baking pan. Using a solid spatula, spread chocolate evenly across the entire pan.
Heat the white chocolate in a heatproof container over simmering water in a saucepan. Heat, stirring often, until melted.
Spoon the white chocolate as evenly as possible over the layer of bittersweet chocolate. Carefully spread it into an even layer, trying to avoid mixing the white and dark chocolate as much as possible. Using a spoon or utensil, swirl the dark and white chocolate together until you’re happy with the marble pattern.
Sprinkle the peppermint candies evenly on top. Refrigerate for 1.5 hours or until firm.
Once the bark is firm, break the bark into shards. They can be as big or small as you like. Store the peppermint bark in an airtight container and refrigerate for up to 3 weeks.
To break up the peppermint bark, use a knife to wedge in between the pan and the firm sheet of chocolate. Gently pull apart from the parchment paper. Use your hands to break up the chocolate, starting out with two or three large shards, and breaking them up into more bite-sized pieces.
You can also heat the chocolate in the microwave following the directions on the package.