In a 1-quart saucepan set over medium heat, combine the cream, milk, and sugar. Place the cornstarch and 1/4 cup of the bourbon in a small mixing bowl and whisk to blend and make a slurry. Pour the slurry into the cream mixture and bring to a boil. Once the sauce begins to boil, reduce the heat to a gentle simmer and cook, stirring occasionally, for 5 minutes. Remove the sauce from the heat, add the salt, and stir in the butter and the remaining 1/2 cup of bourbon. Serve warm.
Makes about 3 1/2 cups