
Place the corn syrup, brown sugar, cocoa powder, cream, salt and vanilla extract in a medium-sized saucepan.
Heat over medium heat while whisking occasionally until the cocoa powder has dissolved, and you get a smooth mix.
Continue to cook the hot fudge sauce until it comes to a boil. Then lower the heat and let it simmer for about 3 minutes.
Remove the saucepan from the heat and add the chocolate chips and butter. Whisk to dissolve.
Transfer the sauce into glass jars and let them cool slightly.
Serve over ice cream while still warm.
Store in the refrigerator, but warm it up gently in the microwave (or in a water bath on the stove), before serving.