In a medium saucepan over medium heat, combine the sugar, brown sugar, heavy cream, butter, vanilla and pumpkin pie spice. Whisk until sugar has melted and mixture has thickened. It will coat the back of a spoon, but not be super thick.
At this stage, whisk in the baking soda.
All the syrup to cool slightly before serving.
If you’ve tried this recipe, come back and let us know how it was!