Begin by preparing a baking sheet. Line it with parchment paper, making sure the paper hangs slightly over the edges for easy removal later.
In a double boiler or microwave, melt the dark chocolate chips until smooth. If using the microwave, heat in 30-second intervals, stirring in between to prevent burning.
Once melted, pour the dark chocolate into the prepared baking sheet. Using a spatula, spread it into an even layer, about 1/4 inch thick. Place it in the refrigerator to set for about 15-20 minutes.
While the dark chocolate is setting, melt the white chocolate chips using the same method as you did for the dark chocolate.
Once the white chocolate is fully melted, remove it from the heat. Stir in the peppermint extract and half of the crushed peppermint candies, reserving the other half for later.
Take the baking sheet out of the fridge and pour the white chocolate mixture over the set dark chocolate layer. Use the spatula to gently spread it out evenly. Be careful not to disturb the dark chocolate layer underneath.
Sprinkle the remaining crushed peppermint candies over the top of the white chocolate layer, along with a pinch of sea salt to enhance the flavors.
Return the baking sheet to the refrigerator for another 30-40 minutes, or until the entire bark is fully set.
Once set, lift the bark out of the pan using the parchment paper overhang. Break it into pieces of desired size.