In a small pan, combine the brown sugar, water, pumpkin purée, pumpkin pie spice, and a pinch of salt. Whisk until well combined.
Bring the mixture to a gentle boil, then reduce the heat to low. Let it simmer for about 10 minutes, whisking occasionally, until the sugar has fully dissolved. Keep it at a gentle simmer, as the goal is a light, thin simple syrup, not a thick caramel.
Strain the mixture through a fine mesh strainer or nut milk bag. Don’t skip this step, as it makes the texture much smoother.
Stir in the vanilla bean paste (or extract).
Enjoy in a pumpkin spice oat milk latte or in your drink of choice! Let remaining syrup cool before transferring it to an airtight jar and storing it in the fridge for up to 2 weeks.