In a large mixing bowl, combine the softened cream cheese and softened unsalted butter.
Using an electric mixer, beat the cream cheese and butter together on medium speed until smooth and creamy, about 2 to 3 minutes.
Add the vanilla extract and salt to the mixture and continue to beat until fully incorporated.
Gradually add the sifted powdered sugar, one cup at a time, beating on low speed after each addition to prevent powdered sugar from flying out.
Once all powdered sugar is added, increase the mixer speed to medium and beat until the frosting is smooth, fluffy, and spreadable, about 2 to 3 minutes.
Use immediately to frost carrot cake or store as directed.