In the bowl of a stand mixer fitted with the paddle attachment, beat butter and salt at low speed until smooth.

In a large bowl, sift together confectioners’ sugar and cocoa. Gradually add sugar mixture, about 1 cup at a time, to butter mixture alternately with cream, about 1 tablespoon (15 grams) at a time, beating until smooth after each addition, stopping to scrape bottom and sides of bowl and paddle. Beat in vanilla. Increase mixer speed to medium, and beat until fluffy, 2 to 3 minutes.