Flawless Buttercream Icing

Cream together the butter and shortening till well combined and smooth. Add salt and vanilla and mix well. Gradually add powdered sugar, mixing well and scraping down the sides of the bowl after each addition. Once all the powdered sugar is incorporated, add the milk and mix well. Whip on high speed until light and fluffy. For a harder crusting icing, increase the powdered sugar to about 4-5 cups. You will also need to then increase the milk to 2-3 Tablespoons. Note that this will result in a thicker, sweeter icing that will develop a harder crust. The softer icing is ideal for filling, frosting, and basic piping (writing messages, borders, leaves etc.) but it will not crust enough to use the paper towel method to smooth the icing. I have successfully piped roses with the softer icing though it is not necessarily ideal for that job as it is quite soft and could be tricky if you don't have experience piping roses. I would recommend the thicker version for roses and other flowers that do not get piped directly onto the cake, and the thicker icing is also suitable for the paper towel method for smoothing the icing.