Line cookie sheet with parchment paper. Place 1 container of frosting at a time in 2-cup glass measuring cup. Microwave uncovered on High 45 to 60 seconds, stirring every 15 seconds, until melted. Dip each cookie in frosting, allowing excess to drip off. Place cookies on parchment paper. Decorate as desired. Let stand until frosting is set, about 1 hour.