Combine the cream cheese and butter on medium speed, just until blended, in the bowl of a stand mixer fitted with the paddle attachment. Stop and scrape down the sides of the bowl. Add the vanilla and salt and beat until combined. With the speed on low, add the powdered sugar in 4 batches, beating until smooth between each addition. Refrigerate for 5 to 10 minutes before using.
Recipe courtesy of Alton Brown, 2011