Use this chocolate frosting in our Cocoa Buttermilk Cake.
Sift sugar, cocoa powder, and salt into a large bowl. Put cream cheese and butter into the bowl of an electric mixer fitted with the paddle attachment; mix on medium-high speed until pale and fluffy, about 4 minutes. Reduce speed to low. Gradually add sugar mixture; mix until combined, 1 to 2 minutes. Mix in chocolate and sour cream. Use immediately.