In a stand mixer fitted with a paddle attachment, beat the butter on medium speed for about 1 minute.
Add the powdered sugar one cup at a time. Stop the bowl to scrape down the bottom and sides of the bowl.
Add the black cocoa powder and mix until smooth.
Add the melted chocolate, vanilla and mix until combined.
Slowly add in the whipping cream. Turn off the mixer to scrape the sides and bottom of the bowl.
Add the black food gel and then mix on medium high speed for 3-5 minutes.
Let the buttercream sit for at least a couple hours or overnight as the color will darken with time.