Hot Fudge Sauce

From Gourmet Magazine February 2004
serve with Frozen Chocolate Caramel Parfaits

2/3 C heavy cream
1/2 C light corn syrup
1/3 C packed dark brown sugar
1/4 C unsweetened Dutch-process cocoa powder
1/4 tsp salt
6oz bittersweet chocolate, finely chopped
2 Tbsp unsalted butter
1 tsp vanilla

Bring cream, corn syrup, sugar, cocoa, salt, and half of chocolate to a boil in a heavy saucepan over moderate heat, stirring, until chocolate is melted. Reduce heat and cook at low boil, stirring occasionally, 5 minutes; remove from heat. Add butter, vanilla, and remaining chocolate and stir until smooth. Cool sauce to warm before serving.