Step 1

In a stand mixer fitted with a paddle attachment, whip the butter on medium speed until creamy and light in color, about 4 minutes. Scrape down the bowl and paddle, then add the powdered sugar, cocoa powders, milk, vanilla extract, and salt. Turn the mixer to low until all ingredients start to come together.

Step 2

Add the black food color gel, increase the speed to medium and beat for two full minutes. The color will resemble wet concrete at first, but will darken as time goes on.

Step 3

Place the buttercream in an airtight container and allow the color to deepen for 24 hours or more.