Whisky Caramel Sauce

Cook sugar in a dry 2-quart heavy saucepan over moderate heat, undisturbed, until it begins to melt. Continue to cook, stirring occasionally with a fork, until sugar is melted into a deep golden caramel. Remove from heat and carefully add Scotch, butter, and salt (caramel will steam vigorously and harden). Cook over moderately low heat, stirring, until caramel is dissolved. Cool sauce to warm.