Using a stand mixer, beat the butter and shortening on medium speed for 1 minute or until creamed with a paddle attachment.
Add sifted powdered sugar, one cup at a time, beat on lowest speed.
Add the heavy whipping cream, continue beating on lowest speed.
Add the vanilla and salt. Beat buttercream on lowest speed for 1 minute. Take the bowl off of the stand mixer, and scrape the sides and bottom of the bowl by hand. Put the bowl back on the stand mixer and continue mixing on lowest speed for 2 minutes.
If you are adding gel food coloring, do this by hand to prevent any air bubbles.
