Place the granulated sugar in a medium, heavy-bottomed saucepan over medium heat. Let it melt, stirring or gently swirling the pan as needed, until the sugar becomes a smooth amber-colored syrup.

Add the butter several pieces at a time and whisk until it is fully melted and combined with the caramel. The mixture will bubble vigorously, so keep your face and hands away from the steam.

Slowly pour in the slightly warmed cream while whisking continuously. The caramel will foam and rise, so use a deep saucepan and add the cream carefully.

Continue cooking at a gentle bubble for about 1 minute, whisking until the sauce becomes smooth and slightly thickened. If it looks temporarily lumpy, continue gentle whisking over low heat until it comes together.

Remove the saucepan from the heat and stir in the salt and optional vanilla extract. Cool the sauce for several minutes before serving, remembering that it will thicken noticeably as it cools.