Place butter, cream, salt, and sugar in sauce pan over medium-high heat.  Whisk continuously. Once this begins to simmer turn the heat down to medium and set timer for 4 minutes.  You want the sauce to “simmer” not turn into a “full rolling boil.”  Cook over medium heat for 4 minutes.  Do not over cook.

After 4 minutes, remove from heat.  Allow to stop bubbling (about 15 seconds) stir in chocolate chips with a wooden spoon.  Next, stir in marshmallows and vanilla.  Continue stirring until combined.   Add nuts if desired.   Transfer into foil lined pan & put in refrigerator to cool.