Achieving the correct consistency for frosting is tricky, especially for an amateur attempting to make the delicious treat from scratch. Royal icing is the standard used by bakers to create a product stiff enough to stand up on cupcakes and other confections. It can take years of practice to perfect a royal icing recipe, which isn't much help when you immediately need cupcakes for a birthday party or bake sale. Stiffen store-bought icing with an ingredient that won't alter its taste, giving you the consistency you require.
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Pour the store-bought frosting into a plastic or glass mixing bowl. Use a wooden spoon or spatula to scrape off the frosting container's sides.
Add 1 tablespoon powdered sugar to the frosting. Work the powdered, or confectioners', sugar into the frosting until it is completely incorporated.
Place a spoonful of the frosting onto a piece of waxed paper. Attempt to create a peak with the frosting using a knife or off-set spatula. If the frosting hasn't reached the desired consistency, place the test amount back into the bowl.
Continue to add more powdered sugar by 1/2 tablespoon, testing the frosting in the same matter after each addition until the desired consistency is reached.