Add sugar and water to a heavy-bottom sauce pan over medium heat. Stir gently until the sugar dissolves.
Stop stirring and bring the mixture to a boil. Allow it to boil for 7-8 minutes without stirring it; it should reach 250℉ on a candy thermometer and will be orange-gold in color.
Add butter. Whisk it in until fully combined, but be careful not to splash it.
Slowly mix in the heavy cream - be careful as it may bubble up - and stir until fully combined.
Add pumpkin spice, cinnamon, and vanilla. Allow the mixture to boil for another 3-5 minutes until it thickens and is glossy. It should be a deep golden-brown color.
Before serving, allow the sauce to cool. Enjoy!
Notes
Use a candy thermometer- this is necessary! Sugar-based sauces like caramel, butterscotch, and toffee are easy to burn if you aren't careful. Use a candy thermometer to make sure you do not burn your sauce and ruin your saucepan.
Add butter and heavy cream very slowly so they do not heat too quickly and curdle, ruining your sauce. You don't want them to splatter, either.
Don't stir while the mixture boils. Let it boil without touching it, then stir once it reaches the correct temperature and color.