Mascarpone, a triple-cream cheese available at most grocery stores, adds a rich, silky component to a frosting. The texture is ideal for holding swoops and creating a snowdrift-like effect when slathered on with an offset spatula.
Let mascarpone stand at room temperature for 30 minutes.
Beat butter and cream cheese with a mixer on medium-high speed until pale and fluffy. Beat in confectioners' sugar, vanilla, and orange zest until combined. Beat in mascarpone until just combined.