Whisk the sugar, cocoa, and cream together in a sauce pan. Cook slowly over medium heat, whisking constantly, until it comes to a gentle boil.

Cook 12 minutes, and remove from heat. Add the chocolate and stir until melted then add in the vanilla. Allow to cool to room temperature.

Beat cream cheese and butter on high until smooth. Add the chocolate mixture to it and beat on medium until well blended.

Refrigerate until it firms a little, but not to long, or you won't be able to frost a cake with it.