Then comes confectioners' sugar, cocoa powder, heavy cream, salt, and vanilla. Beat 1 minute on high after 30 seconds on low speed to avoid powdered sugar flying around.
Adjust buttercream thickness using 1/4 cup confectioners' sugar or cocoa powder. In thick buttercream, add 1–2 tablespoons coconut milk or heavy cream.
To bring the buttercream to room temperature, leave it on the counter for at least an hour (or more, depending on how chilly it is). Spreading and piping will be easy.