In a large bowl, beat unsalted butter with an electric mixer until light and fluffy. With mixer on low, gradually beat in the powdered sugar, cream and vanilla until completely combined.
Then gradually beat in the cocoa powder with an electric mixer on low speed until combined. Then turn up to medium-high speed and beat until fluffyl
Next, add the black cocoa powder and beat on low until combined. Continue beating on medium speed until smooth. Add the black food gel to the black chocolate icing and stir until combined.
Notes
If the frosting is too thick, you can add more cream. Just add one tablespoon at a time, then mix thoroughly until you get the consistency you like. It should be smooth and shiny.