Line a 1~2 inch deep baking sheet/ brownie pan with parchment or wax paper.
In a microwave-safe bowl, melt the dark chocolate in 30-second intervals, stirring well after each, until smooth. Stir in half of the peppermint extract.
Pour the melted dark chocolate onto the prepared baking sheet and spread it into an even layer, about 1/4 inch thick. Place the pan in the refrigerator for about 20-30 minutes, or until the chocolate is firm.
In another microwave-safe bowl, melt the white chocolate using the same method. Stir in the remaining peppermint extract.
Stir about 3/4 cup of the crushed peppermint candies into the white chocolate mixture.
Pour the white chocolate mixture over the chilled dark chocolate layer and spread it evenly.
Immediately sprinkle the remaining crushed peppermint candies over the top of the white chocolate layer.
Return the pan to the refrigerator for at least 30 minutes, or until completely firm.
Once set, break the bark into irregular pieces. Store in an airtight container in the refrigerator for up to a month.