Heat a heavy bottomed sauce pan over medium heat. Add brown sugar, butter, kosher salt and heavy cream. Bring to a boil and cook for 6 to 8 minutes, stirring every 30 seconds, until amber colored and thickened. It will continue to thicken as it cools.
Remove from the heat and stir in vanilla extract and pumpkin pie spice. Store in an airtight container in the refrigerator for up to 2 weeks.