Ensure the butter is softened to room temperature. Sift the confectioners' sugar to remove lumps. Measure out the black cocoa powder.

In a large mixing bowl, use an electric mixer to cream the softened butter until smooth and fluffy.

Gradually add the black cocoa powder to the creamed butter. Start the mixer on low to prevent cocoa powder from flying, then increase speed as it incorporates.

Begin adding the sifted confectioners' sugar, one cup at a time, mixing well after each addition. Add vanilla extract and a pinch of salt. Continue mixing.

Depending on the desired consistency, add heavy cream or milk one tablespoon at a time until the buttercream reaches the preferred smoothness.

Beat the mixture for an additional 2-3 minutes on medium-high speed until the buttercream becomes light and fluffy.

Taste the buttercream and adjust sweetness or cocoa intensity if needed by adding more sugar or cocoa powder.