01 - In a medium, heavy-bottomed saucepan, heat the sugar over medium heat. Stir constantly with a heat-resistant spatula or wooden spoon as the sugar melts, clumps, and then turns into a golden-brown liquid.
02 - Once all the sugar has melted and the caramel reaches a deep amber color, carefully add the butter cubes. The mixture will bubble vigorously—keep stirring until the butter is completely melted and incorporated.
03 - Slowly pour in the heavy cream while stirring. The mixture will bubble up again; continue to stir until smooth and fully combined.
04 - Remove from heat. Stir in the salt and vanilla extract if using.
05 - Allow the sauce to cool for 10–15 minutes before using. The caramel will thicken as it cools.