How to Make It
Line a large rimmed baking sheet (18 x13-inch) with parchment paper, allowing 4 to 5 inches to extend over short sides.
Arrange cookies in a single layer in prepared sheet, breaking to fill any holes. (You may have some wafers left over.)
Place white chocolate and oil in a microwave-safe bowl; microwave on MEDIUM (50% power) until chocolate melts, about 1 minute, stirring every 20 seconds. Stir in peppermint extract.
Place semisweet chocolate in a microwave-safe bowl; microwave on MEDIUM (50% power) until chocolate melts, about 3 minutes, stirring every 20 seconds. Spread semisweet chocolate evenly over wafer cookies; dollop with white chocolate mixture, and, using a knife, swirl chocolate mixtures together. Chill until firm, about 45 minutes.
Lift bark from pan using parchment paper as handles; cut or break into 2-inch pieces. Layer between sheets of wax paper in an airtight container, and store in refrigerator for up to 1 week.