In a medium size sauce pan, heat the sugar and mix constantly using a wooden spoon or a heat resistant spatula.
Stir constantly until the sugar turn into a golden color or brownish color. Be careful not to burn the sugar.
Once the sugar is completely melted, add in the butter immediately and make sure that mixture will not turn into clumps. If it does, remove the pan from the heat and gently but quickly stir to combine the mixture again.
This may take a few minutes, but if you continue whisking they will combine again.
If the mixture has combine, add the heavy cream slowly. After the cream has been added, stop stirring and let the sauce boil for 1 more minute. Since the cream is colder than the caramel, the mixture will rise higher to the pan, so be careful not to get burned.
Turn off the heat and add the salt. Mix and let cool.
Store the sauce in an airtight container.