Measure all ingredients and place them near the stove. Heat sugar over medium-high heat in a medium sized, heavy bottomed saucepan with high sides. Once sugar begins to melt, gently stir with a heatproof spatula or whisk to help it heat evenly.
When (nearly) all of the sugar has melted and liquid is amber (caramel) colored, add the butter and stir until it has completely melted. CAUTION: hot mixture will bubble up when you add the butter.
Remove from heat and stir in the cream. Again CAUTION, the mixture will foam up considerably and possibly splatter. Keep stirring until caramel sauce is smooth.
To remove any undissolved crystals, pour sauce through a wire sieve into a clean, heatproof container. Stir in vanilla and salt if desired.
Caramel sauce will thicken as it cools. Store tightly covered in the refrigerator for up to two weeks. Gently heat caramel sauce on the stove or in a microwave before serving.
Notes
Tips:
This recipe will only work if you start with a thin layer of sugar: it's essential you use a medium-sized saucepan for the amount of sugar in the recipe above. If you want to make more caramel, do it in two batches.
Be careful not to burn yourself! Molten caramel is hotter than you can imagine. It will bubble up and possibly splatter when you add the butter and again when you add the cream so use a pot with higher sides. Handle the caramel with caution and use heatproof utensils. If you must taste, use a cold spoon and test the temperature of the caramel with your finger before you put it in your mouth.