Bourbon Salted Caramel Sauce is what every great caramel should be; just sweet enough, velvety smooth, slightly smoky, and a gorgeous deep amber brown colour.
Sprinkle the sugar evenly over the bottom of a heavy-bottomed saucepan of at least 2 quarts but preferably 3 quarts in capacity. Place the sugar over medium high heat and whisk as it begins to melt and clump. Continue whisking until all of the sugar is melted and then remove the whisk and swirl the pan from time to time until it reaches a deep amber colour or 340°F to 350°F.
Add the softened butter carefully and all at once; it will bubble furiously. Whisk until the butter is incorporated and remove from the heat.
Whisk in the heavy cream and then the bourbon and salt carefully as it will bubble furiously again. When it stops bubbling, set it aside on a cool burner or a trivet for 10 minutes before transferring to a heat-proof jar. As it cools, it will thicken. Store the Bourbon Salted Caramel Sauce tightly covered in the refrigerator for up to 1 month.
To reheat, remove the lid and microwave in 10 second bursts, stirring after each one until the caramel is smooth, pourable, and warm but not hot. Alternatively, you can place the covered jar in a container of hot tap water for several minutes, or until the caramel is smooth and pourable when stirred.