The sauce will keep in the refrigerator, in an airtight container, up to one week. Reheat it before serving.
¾ cup whipping cream
1 tsp. vanilla extract
1 cup sugar
3 Tbs. dark corn syrup
4 Tbs. unsalted butter (½ stick), cut into 8 pieces
Combine cream and vanilla in measuring cup. Set aside.
In a heavy, deep saucepan, combine sugar and corn syrup. Cook over medium-high heat, stirring with a wooden spoon until sugar is uniformly moist. Continue cooking, stirring occasionally, until mixture is color of strong tea, about 6 minutes. Take care, as it quickly starts to burn. Immediately remove pot from heat and whisk in butter; mixture will sputter. As soon as butter melts completely, pour in reserved cream.
Whisk until congealed sugar has dissolved. Cook, over low heat, until sauce looks creamy and smooth, stirring constantly around edges and bottom, 1 to 2 minutes. Pour hot sauce carefully into heatproof container. It will thicken as it cools. Sauce will keep up to a week, tightly covered. Warm before serving.