In a heavy saucepan, over medium heat, combine cream, corn syrup, brown sugar, cocoa pwd, salt, and half the chocolate chips.

Bring the mixture to a low boil, stirring/whisking constantly, until the chocolate chips melt and the mixture is smooth.

Reduce heat to simmer, and continue to cook for about 5 minutes, stirring often.

Remove from heat and stir in butter, vanilla, and remaining chocolate chips. Whisk until melted and smooth.

Pour into heat proof jar, such as a canning jar.

Sauce will continue to thicken as it cools.

Sauce may be reheated, but I recommend only reheating what you'll be using, not the entire jar.

Store in refrigerator.