In a small saucepan over medium heat, cook sugar, lifting, swirling, and tipping pan often, until it melts, turns deep amber, and begins to smoke, 10 to 12 minutes. Remove from heat and carefully pour in whipping cream (sugar will seize up), along with butter and salt.
Return to medium heat and cook, stirring, until sugar melts again, 5 minutes. Remove from heat and stir whiskey. Let cool to room temperature.
*Much of the alcohol burns off when the whiskey goes into the hot sauce, but you can substitute cream if you prefer.
Make ahead: Up to 1 week, chilled; bring to room temperature to serve.