Stir sugar, 1 tablespoon whiskey, corn syrup,and 1 tablespoon water in a medium deep saucepan over medium-low heat untilsugar dissolves.
Increase heat, bring to a boil withoutstirring, and cook, occasionally swirling pan and brushing down sides with awet pastry brush, until sugar is deep amber in color, 6–8 minutes.
Remove caramel from heat; whisk in remaining 1/4 cup cream, butter, and salt (mixturewill bubble vigorously).
Let cool for 5 minutes; whisk in theremaining 1/2 Tbsp. whiskey and vanilla.Let the whiskey caramel cool slightly.