There's a perfect consistency necessary to make frosting that's perfect for cake, cake layers and cupcakes. You can't achieve it if your frosting's thin or or if it's too thick.
Why's your frosting thin?
First, the issue may be that your kitchen is too warm making for warm frosting that is loose and runny. Because frosting is primarily comprised of oil or fat, it can easily become runny and thin at higher temperatures.
The temperature of your butter is one of the keys to success in making smooth, delicious frosting. I recommend removing it from the fridge at least an hour or more before you begin making the frosting. You want butter that is soft but not melted or greasy.
If your frosting is not thin due to the heat, it could be a result of too much liquid. Double-check your recipe to see how much milk is called for in the ingredients.
If your frosting has been at room temperature, or your kitchen is warm from the oven, simply cover the top of the mixing bowl with plastic wrap, and place it in the fridge for 30 minutes.
If you need to thicken the frosting, powdered sugar or cocoa are two ingredients, depending on the flavor, you can use. Only do a little at a time!
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