When the sugar completely melts and turns to amber color, remove the sugar from the heat. Don’t overcook the sugar, otherwise, it will have a bitter taste. Immediately add the heavy cream gradually and stir at the same time. At this stage, the heavy cream will make the sugar bubble so be careful not to burn yourself. Stir with a whisk until the sauce is smooth-it shouldn't take more than 1 minute. However, if there are lumps, place the saucepan over low heat and whisk continuously. Keep stirring until it is smooth and there are no lumps. It may take time to smooth the lumps but in the end, they all go and you have a smooth sauce. (If you are not sure about the lumps, you can strain the caramel to make sure.) Remove from the heat. If you want to make a salted caramel sauce, add the salt and stir.