Hot Fudge Sauce for Jimmy Fallon's Late Night Snack Ice Cream Cake

Place heavy cream and corn syrup in a medium saucepan; bring to a boil over medium-high heat, stirring, about 2 minutes. Remove from heat and stir in chocolate; whisk until melted and well combined. Stir in vanilla and salt. Transfer fudge sauce to a glass container and let cool at room temperature until thickened, about 1 hour.