In the bowl of a stand mixer or using a handheld electric mixer, beat butter at high speed for three minutes until light and fluffy.
Mix in cocoa powder.
Mix in powdered sugar a little bit at a time.
Mix in vanilla and salt.
Pipe over or spread onto desserts.
Notes
Frosts 24 cupcakes or a two layer 8" round cake. Double the recipe if you like your cupcakes with really tall frosting swirls.Add more powdered sugar (confectioners' sugar) as needed if you want a stiffer buttercream.The frosting lasts for up to a week at room temperature or months in the freezer.If frozen, you will need to bring it to room temperature and mix it again for a minute or two before you start piping.