Melted dark and white chocolate drizzled on top of cookies is a special treat. Place the chocolate in a microwave-safe bowl and microwave on High for 1 minute. Stir well, then continue microwaving on High in 30-second bursts until two-thirds of the chocolate has melted, stirring well after each burst. Remove the bowl and continue stirring until all the chocolate has melted. Cool for 5 minutes at room temperature. Use a pastry bag fitted with a fine writing tip to pipe the melted chocolate or dip tines of a fork in chocolate and drizzle.