PREHEAT oven to 350F; Generously grease two 9 inch round cake pans with solid vegetable shortening, then dust with flour, shake out the excess flour; Set aside.
COMBINE the cake mix, cocoa powder, buttermilk, vegetable oil, eggs, and vanilla in a large mixing bowl; Blend with an electric mixer until the batter is thick and smooth; Pour into prepared pans.
BAKE the cake until it springs back when lightly pressed with your finger, approximately 35 minutes; Cool cakes in pans on wire rack for 30 minutes more and then slip both cakes out of the pans into your freezer; (Frozen cakes are much easier to frost.) Now you can prepare the frosting.
COMBINE cream cheese and butter with your electric mixer on low speed until fluffy, stop the machine; Add the confectioners’ sugar; Continue to blend on low until the sugar is well combined; Add the orange juice and zest, Increase the speed and beat until frosting is light and fluffy; Use at once to frost cake.