Be careful when working with hot caramel; never touch or taste it until it has cooled fully.
Heat sugar, salt, and water in a heavy-bottomed pan over high heat until the mixture starts to color around the edges. Lower heat to medium and swirl mixture until it turns light brown. Remove pan from heat, and whisk in butter, then the cream, in small amounts. (Be careful: the cream may spatter.) Let cool, then transfer to a heat-proof serving dish. Store sauce in the refrigerator.