Bring cream, corn syrup, sugar, cocoa, salt, to a boil in a 1 quart heavy sauce pan. Reduce heat and simmer, stirring continuously for 5 minutes. Add butter, chocolate and vanilla and stir until melted. Remove from heat and pour into mason jars. Allow to cool. Serve immediately or keep in your refrigerator until ready to use.
Hot Fudge Sundae:
Pour warm hot fudge over scoops of The Best Vanilla Ice Cream or Vanilla Coconut Cream Ice Cream and top with whipped cream, slivered almonds and a cherry.