Layered Peppermint Bark

Line a 9x12 inch baking pan with aluminum foil or parchment paper.
Melt half of the white chocolate in the top of a double boiler over just barely simmering water, stirring frequently and scraping down the sides with a rubber spatula to avoid scorching. Spread the white chocolate into the prepared pan. Sprinkle 1/4 of the crushed peppermints evenly over white chocolate. Chill until firm, about 15 minutes.
Meanwhile, melt the dark chocolate, heavy cream, and peppermint extract together in the top of a double boiler over just barely simmering water, stirring frequently, until just melted. Quickly pour the chocolate layer over the chilled white chocolate layer; spread evenly. Chill until firm, about 20 minutes.
Meanwhile, melt the remaining white chocolate in the top of a double boiler over just barely simmering water, stirring frequently, until just melted. Spread quickly over the chilled bark. Sprinkle with the remaining peppermint pieces; chill until firm, about 20 minutes. Cut or break into small pieces to serve.