In a small saucepan, combine the brown sugar, water, cinnamon and salt. Warm over medium heat, stirring, until the sugar fully dissolves, about 2 to 3 minutes.
Let it bubble gently for 2 minutes, then remove from the heat and stir in the vanilla. Let the syrup cool for 10 minutes.
Brew 2 shots of espresso and let it rest for about 30 seconds.
Add the espresso, 1 to 2 tablespoons of syrup, ¼ teaspoon cinnamon and about 1 cup of ice to a shaker or mason jar.
Close the lid tightly and shake hard for 15 to 20 seconds, until the outside is very cold and the liquid looks pale and foamy.
Fill a tall glass with fresh ice and pour the shaken espresso over it.
Slowly pour the milk over the top and watch it swirl.
Add a pinch of cinnamon on top if you like, and serve right away.