How To Get Store Bought Frosting To Harden. Continue until your desired consistency is achieved. About 30 to 45 seconds should be enough time to microwave the frosting.
Use a hand mixer to incorporate 1 tablespoon of confectioners’ sugar into your icing. You might want to add some powdered sugar to thicken it up. If the frosting is not as smooth as you want, open the microwave and stir it.