This frosting works well with carrot cake or applesauce cake.
In the bowl of an electric mixer fitted with the paddle attachment, beat cream cheese on medium-low speed until smooth, about 1 minute. Add the butter, and beat until smooth, 2 minutes more.
On low speed, add the confectioners' sugar; mix until completely combined. Transfer filling to an airtight container, and chill until firm, 4 hours or overnight. Store, refrigerated, up to 3 days.