Before you start, make sure that anything that will touch your melting chocolate is bone-dry; a small drop of water can cause the whole thing to seize up. Also, take extra care when melting the white chocolate and follow the directions closely as it can burn easily; you want the water bath to be gently steaming, not simmering.
Fill two smallish saucepans with 2 inches of water and bring both to a bare simmer. Turn off the heat. Place the dark chocolate in a medium-sized heatproof bowl and set over a steamy pot of water. Place the white chocolate in a small heat-proof bowl and set over the other pot. Stir the chocolates occasionally until smooth and melted, 3-5 minutes. Add a few drops of peppermint extract and 1 teaspoon of the coconut oil to the white chocolate and stir to combine and melt the coconut oil. Place the 1/4 teaspoon peppermint extract and remaining 2 teaspoons coconut oil in the dark chocolate and stir to combine and melt the coconut oil.
Line a small (9x12") baking sheet with parchment paper. Carefully remove the bowl of dark chocolate (pull it toward you quickly to avoid a steam burn from the hot water beneath) and dry the bottom of the bowl on a kitchen towel; this will prevent steamy water drops from marring your bark as you pour the chocolate. Scrape the dark chocolate mixture onto the parchment and spread it to 1/4" thickness. Remove the bowl of white chocolate in the same manner, and use a teaspoon to dollop the white chocolate mixture evenly over the dark chocolate in round pools. Use the tip of a chopstick or wooden skewer to swirl the chocolates together. While the chocolate is still soft, sprinkle evenly with the candy cane pieces, cacao nibs and flaky salt.
Place the bark in the refrigerator until firm, about 30 minutes. Remove from the refrigerator and use the tip of a butter knife to break up the bark into rough 2-inch pieces. Store refrigerated airtight or at cool room temperature for up to 1-2 weeks.
Be sure to use chocolates that you like the flavor of on their own. For dark, I like Guittard, Scharffenberger, Recchiuti and Tcho's bittersweet chocolates. My white chocolate of choice is organic Green and Black's, which is rich with cacao butter and flecks of vanilla bean.Big pieces of candy cane look pretty, but smaller bits are easier to eat; I try to find somewhere in the middle.This makes a smallish batch of bark; feel free to double the recipe and spread it onto a larger baking sheet.I like the hint of coconut flavor the oil adds here, but I think you could use butter, ghee, or a neutral vegetable oil (grapeseed or sunflower) in its place.Peppermint extracts vary in strength, so start with less if using a different brand than Frontier.Nutritional values are based on one of eight servings.