Combine sugar and water in a small heavy saucepan over medium-high heat; cook until sugar dissolves, stirring constantly. Cook an additional 15 minutes or until golden (do not stir). Remove from heat. Carefully add butter and cream cheese, stirring constantly with a whisk (mixture will be hot and bubble vigorously). Cool slightly, and stir in whiskey and milk.
Note: Substitute 1 tablespoon imitation rum extract and 3 tablespoons water for the Irish whiskey, if desired.