Add the brown sugar, pumpkin puree, pumpkin pie spice, salt and 1 cup of water to a small saucepan.
Bring to a simmer and stir until the sugar has dissolved, about 10 minutes. Remove from heat and let cool. The syrup can be made and stored in the refrigerator for up to 2 weeks in advance.
For the latte:
Shake the syrup before using. Add 2 tablespoons (40g) of the pumpkin spice syrup to a mug and add steamed milk over the top, followed by espresso shots. Garnish with a sprinkle of cinnamon (optional). Serve immediately.