Bring a shallow pan of water to a simmer. Add the white chocolate to a heatproof bowl and set over the simmering water to melt. Stir in the peppermint extract.
Dip the cookies one by one in the melted chocolate to cover completely, then transfer to a parchment-lined baking sheet. Sprinkle the crushed candy over the tops. Allow the cookies to set and dry before serving.