Place all ingredients other than the vanilla extract into a medium saucepan.
1 1/2 cup heavy cream, 1 1/2 cup sugar, 6 ounce nearly unsweetened (95%) chocolate, chopped, 3 tablespoon unsalted butter, 3 tablespoon light corn syrup, 1 teaspoon vanilla bean paste, 1/2 teaspoon salt
Stir over low heat until the chocolate and butter are completely melted and the color is homogeneous.
Increase the heat to medium and bring the mixture to a boil, stirring often.
Continue to boil for about 8-10 minutes until the mixture has thickened and reduced.
Remove from the heat and cool slightly before stirring in the vanilla extract.
1/2 teaspoon vanilla extract
Transfer to a heat-proof storage container (such as a large mason jar). Use immediately, or store in the refrigerator until ready to use. Heat the sauce in the jar in the microwave for about 30 seconds at a time until it is pourable before using.