Wait until the sugar begins to melt. Take a spatula and gently stir to mix melted and still solid sugar. Sometimes people recommend not touching the sugar until melted. However, you better keep yourself busy with stirring. In addition, the sugar will not burn because you watch it closely. (Be careful with the spatula as there will also be sugar crusts building up.)
Watch your pot! The melted sugar will soon start to darken. It may not turn too dark, though. Let it become like golden honey or amber. Too light in color and it will not taste like caramel. But be careful. Once it's becoming dark it can turn too dark or even burn in seconds!
After it is finished take it from the heat. Put the butter in and stir until it is melted and incorporated. Then stir in the whipping cream (or condensed milk) in portions. Add salt and stir well.
Put the Caramel Sauce in a clean jar and keep it in the refrigerator. It will be harder when cool. So take it out an hour before you drizzle it over desserts. The caramel sauce keeps fresh for about two weeks.