Add unwrapped candy canes to a large plastic bag (or 2; the peppermint has a tendency to rip through plastic bags as it is crushed). Seal the bag without air, and crush with a rolling pin or meat mallet until coarse crumbs are formed. Set aside.
Line an 8x8 or 9x9-inch pan with parchment paper, leaving an overhang for easy removal. Set aside. Coarsely chop the white, semi-sweet, and milk chocolate. Tip: Be patient when melting the chocolate and avoid rapid temperature changes (don’t microwave too long or excessively, stir too much, or refrigerate/freeze layers of finished bark).
Add all except 2 tablespoons (see note 2) of the chopped semi-sweet and milk chocolate to a large microwave-safe bowl. Add 1/2 teaspoon oil. Microwave for 15 seconds, then stir vigorously for 15 seconds. Continue until chocolate is mostly melted. You never want the chocolate to get hot, just warm enough to melt gradually; once it's smoothly melted, it should be room temperature.Once chocolate is mostly melted, add the set-aside 2 tablespoons of chocolate and stir until it melts. Be patient and don’t microwave unless it isn’t melting after stirring for 1 minute. (Then microwave in bursts of 5 seconds.)
Once chocolate is fully melted and smooth, pour in the peppermint extract (use 1/2 tsp for a stronger peppermint flavor) and mix to combine. Pour the chocolate mixture into the prepared pan and smooth in an even layer with a spatula. Do not refrigerate. Set aside at room temperature.
Add all except 2 tablespoons of the chopped white chocolate to a large microwave-safe bowl. Add 1/2 teaspoon oil. Follow the directions above for melting. Add the reserved 2 tablespoons white chocolate and mix until melted. Once smooth, drizzle evenly on top of the chocolate base layer until all the chocolate is poured on top. Carefully and slowly smooth the white chocolate into an even layer with the back of a spoon, being careful to not swirl the two layers together. Immediately, sprinkle the crushed candy canes on top (add as much or as little as you’d like). Set aside at room temperature (not in the fridge) until the bark is completely hardened, about 3–5 hours.
Once hardened, remove from the pan using the overhang. Break or cut (see note 3) into pieces as big or small as you’d like. Enjoy!
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Notes
Note 1: To make peppermint bark that doesn’t separate, streak, discolor, or become crumbly, you’ll want to grab high quality baking bars. Other forms such as chocolate chips/baking morsels have stabilizers that keep them from melting completely smooth, and their layers may separate when you break or cut the bark.Note 2: Melting the chocolate slowly and stirring frequently prevents streaks by keeping the cocoa butter from separating. Adding unmelted chocolate at the end helps cool and stabilize it, creating a smooth, glossy finish that sets well and resists melting on fingers.Note 3: If you’d prefer to cut the bark instead of break it, use a large, sharp knife. Run the knife under very hot water, dry it with a kitchen towel, and make a quick and decisive cut. Repeat this process for each cut you make.Storage: Store in a tightly sealed container in a cool, dark place at room temperature for up to 2 weeks. It does not need to be refrigerated.