For salted caramel sauce: Add 1/2 teaspoon fine sea salt (more to taste)
In a medium sauce pan, heat sugar over medium heat. Stir every minute (about 5-7 minutes) with a whisk, spoon or rubber spatula. The sugar will first get clumpy and then start to melt into a liquid.
When the sugar has turned to a liquid, reduce the heat to medium-low. Add butter right away. Grab a new spoon and keep stirring until butter is completely melted and bubbly (about 1-2 minutes).
Slowly pour in heavy cream until it comes to a boil. Then remove from heat and stir constantly for one minute. Add salt if desired. Then let cool for a few minutes in the pan and then transfer to a jar. It will thicken as it cools.
Store in a mason jar for up to 3 weeks in the refrigerator. Warm in the microwave 30 seconds before serving.