Source  Mel's Kitchen Cafe

Recipe Added:  12/14/2011

Mix sugar, cocoa and salt in a large, heavy saucepan. Whisk in the water until well blended. Bring to a simmer over medium-high heat, stirring constantly. Remove from the heat and whisk in the cream, corn syrup, vinegar and 1/3 cup chopped chocolate.

Return to medium-high heat and boil. Whisk frequently until the bubbles become small and the syrup is thick and sticky, 5-7 minutes (or 225 degrees on a candy thermometer). Remove from the heat and add the rest of the chopped chocolate, butter, and vanilla. Whisk until smooth. Serve at once, or let cool. Cover and refrigerate up to 2 weeks. Reheat over low heat or in the microwave on 50% power.

1. http://www.melskitchencafe.com/2009/07/hot-fudge-sauce.html