Combine the sugar and water in a stainless pot. Wash down any crystals from the inner sides of pot with a clean brush, dipped in cold water to prevent crystallization. Bring the mixture to boil and cook until sugar is caramelized. When the syrup is mahogany brown, add the butter and swirl the pan. Carefully pour in the heavy cream and let the mixture return to boil. Strain the caramel sauce into a container over an ice bath.