In a large bowl, beat butter with a mixer at medium speed until creamy. In a small bowl, sift together confectioners’ sugar, cocoa, and salt. Add cocoa mixture to butter, beating until combined. Stir in buttermilk until mixture reaches a spreadable consistency.
Recipe by Southern Cast Iron at https://southerncastiron.com/vanilla-buttermilk-cake-with-chocolate-buttermilk-frosting/