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