Add the icing sugar and butter to a bowl of a stand mixer fitted with a paddle attachment. Beat at medium speed until the mixture resembles fine breadcrumbs.
Add the cubed cream cheese and beat at medium-high speed until the frosting is smooth and fluffy. Scrape down the sides of the bowl and mix again for about 2 minutes.
Add the dulce de leche, vanilla, and salt and beat again at high speed.
Scrape down the sides of the bowl with a rubber spatula and beat at medium-high speed for a further 3 minutes or until the frosting is light and fluffy. The frosting is now ready to use on cakes or cupcakes.