How to Make It
Combine butter and chocolate in a small saucepan; cook over low heat until chocolate melts, stirring occasionally. Combine sugar and cocoa in a medium bowl; add corn syrup and milk, stirring with a whisk until well-blended. Add cocoa mixture to saucepan. Bring to a boil over medium heat, and cook 1 minute, stirring constantly. Remove from heat; stir in vanilla.