In a 2-quart heavy-bottomed saucepan, whisk together sugar and ¼ cup (60 grams) water until smooth. Cook over medium heat, without stirring, until melted and a golden-amber color. Remove from heat. Add butter, 1 tablespoon (14 grams) at a time, whisking until combined after each addition. Add cream and whiskey, and stir to combine. Return mixture to medium heat, and cook, stirring frequently, for 3 to 4 minutes. Stir in salt, and remove from heat. Let cool slightly before serving. If caramel cools completely, it will thicken. Simply reheat it to loosen, if needed.