Place the cream cheese into a mixing bowl. Add mascarpone OR heavy cream to the bowl along with SIFTED powdered sugar
Whip it. It's easy but you need to do it without spending too much time on it (it will only take around 2-3 minutes). So, whip it up with an electric hand mixer.
Add the vanilla, if desired. When the frosting reaches a fluffy, pipeable consistency, stop right there and do not overmix. If you continue beating the frosting, it will separate and gets runny.
The frosting should be stable enough to pipe or frost the cake at this point, however, it will even further set refrigerated
Top Tip: Besides not over whipping and using the right ingredients, the best way to thicken cream cheese frosting is to refrigerate it for 30-60 minutes before using