In a medium saucepan, bring sugar and water to a boil over medium heat. Cook without stirring until the mixture is amber colored, about 10 minutes. Brush the sides of the pan with water as the mixture cooks to prevent the formation of sugar crystals.

Remove the pan from the heat and carefully whisk in butter, cream, vanilla, salt and pumpkin pie spice. Careful: the mixture will boil vigorously during this step.

Let sauce cool completely before serving. Cover and keep in the refrigerate for up to a week. Warm or bring to room temperature before serving.