In a heavy gauge stainless steel pot, cook sugar over medium heat. Stir it constantly with a wooden spoon.
The sugar will develop clumps and then melt into a liquid with an amber color.
After the sugar has melted, decrease the heat to low and stir in the room temperature unsalted butter. Caution: the butter may cause the sugar to bubble.
If the butter starts to separate or the sugar develops clumps again, remove from the heat and whisk it. When it returns to a combined state, return to the heat.
Slowly add the room temperature heavy cream. Caution: it will bubble.
Stop stirring and increase the heat to medium and allow it to boil for 1 minute.
Remove the pot from the heat and stir in the salt.
The caramel will be thin but become thicker as it cools.
Pour the caramel sauce into a glass jar and cover it with a tight lid.
The caramel is stored in the refrigerator, and it will become solid. The caramel can be reheated in the microwave before serving.