Add cocoa powder to melted butter and mix until combined. Add salt, vanilla, and milk; mix well.
Slowly add the powdered sugar; beat until thoroughly combined. If the frosting is too thin for your liking, add additional powdered sugar (a little at a time). If frosting is too thick, add a little bit of milk (a little at a time).
Recipe Source: My Mom
Mom's Chocolate Buttercream Frosting https://www.thegratefulgirlcooks.com/chocolate-buttercream-frosting/