Bring the butter and heavy whipping cream to room temperature by leaving them sit out or using the microwave. Get a whisk ready and set aside.
Put the white sugar in a sauce pan with high sides and place on the stove over medium low heat. Do not stir until you see the the sugar around the edges start to melt and turn brown. Be patient, this could take up to 5 minutes.
Once the sugar starts to melt, stir occasionally with a wooden spoon so that the sugar melts evenly. As the sugar starts to melt, it will clump first. That's normal. The more the sugar melts, the more you'll want to stir.
Continue stirring until only a few large clumps of sugar remain. Break those up with the spoon. Remove the pan from the heat once the sauce reaches 225℉ (or no more than 30 seconds after all sugar has dissolved.)
Have the whisk ready. CAREFULLY pour in ¼ of the cream. The mixture will violently bubble up and that's normal. Whisk quickly until the mixture calms. [Take care to make sure you are whisking the entire pan or globs of caramel may form at the edges of the pan.] Add the next ¼ of the cream and whisk quickly. Keep repeating until all cream has been incorporated.
Add the salted butter 1-2 tablespoons at a time. Whisk quickly until all butter has melted and been incorporated.
Add the salt and whisk until incorporated.
Using a funnel, carefully pour the liquid caramel into storage jars (or decorating bottles) to cool. [If any chunks have formed, place a strainer over the funnel and strain the caramel through a strainer while pouring into the funnel.]
Allow the caramel sauce to come to room temperature before using or placing in the refrigerator.
Refrigerated caramel sauce becomes thick. To return refrigerated caramel back to a sauce, microwave the caramel in increments of 10-15 seconds until desired fluidity is reached. Caramel sauce heats and becomes liquid very, very quickly.