1. In a small saucepan, combine sugar and cream; bring to a boil over medium heat, stirring occasionally.  Reduce heat, and simmer for 6 minutes.  Add chocolate and butter, and stir until melted.  Pour into a bowl, and stir in vanilla.

2.  Let frosting cool, whisking gently from time to time, while you bake the cake.  Don't overwhip, or you'll create air bubbles.

 3.  When cake layers have cooled, check frosting.  It shoujld have the consistency of mayonnaise.  If it is still too thin, allow to cool longer.