Bring brown sugar, corn syrup, butter, and salt to a boil in a medium saucepan over medium-high heat, whisking to dissolve sugar. Boil until mixture is syrupy and measures 1 1/3 cups, about 3 minutes. Remove from heat; add cream and bourbon, if desired, and stir until smooth. Let cool. DO AHEAD: Can be made 3 days ahead. Let cool completely, cover, and chill. Rewarm before serving.