In a heavy-bottomed saucepan over medium heat, add the sugar. Stir constantly with a heat-resistant spoon or whisk. It will clump before it melts—keep stirring! Once the sugar is fully melted and amber in color, be careful not to burn it.
Carefully add the butter. The mixture will bubble rapidly, so be cautious. Stir until the butter is fully melted and combined with the sugar.
Slowly pour in the cream while continuing to stir. The sauce will bubble again—this is normal. Keep stirring until it comes together into a smooth, creamy caramel sauce.
Remove from heat and stir in the salt. Let the sauce cool for 10–15 minutes before transferring it to a jar.