Don't skip the step of sifting the powdered sugar. It is an important step in creating a super creamy and lump-less icing.
In the bowl of a stand mixer fitted with the paddle attachment, mix the cream cheese and butter on medium speed until fully mixed and no lumps remain, 2–3 minutes. Scrape down the sides of the bowl with a spatula. Add powdered sugar, 1 cup at a time, and mix on low speed to start, increasing speed as the sugar is incorporated, for about 4 minutes total. Scrape the bowl after each addition.
After all the powdered sugar has been added and the icing is completely smooth and lump-free, add the vanilla paste and salt. Mix briefly to combine.
Set the icing aside at room temperature until you’re ready to use it. You can make the icing well ahead and store it in the refrigerator but it does set up as it chills. You’ll need to soften it in the microwave and re-whip it before applying it to your cake. Otherwise, the icing will be hard and difficult to spread on a fresh cake without tearing it.