Prepare the frosting: In the bowl of a stand mixer fitted with a paddle or, if using a hand mixer, in a large bowl, combine the cream cheese, butter, vanilla and salt. Beat on medium to medium-high speed until well combined and fluffy, about 1 minute. Turn off the blender and add 1 cup of icing sugar. Starting at low speed and increasing to medium, beat to combine, then turn off the blender. Add the remaining icing sugar, about 1 cup at a time, and beat, starting on low and increasing to medium, until the icing is foamy and starting to harden, about 2 minutes, scraping the sides together. need. Cover and refrigerate frosting for at least 1 hour or until ready to use.