First, make the syrup: In a small cup or jar, mix together the boiling water, brown sugar, cinnamon, and vanilla extract. Whisk until combined although the cinnamon won't fully dissolve. Set aside to cool.
Next, make the brown sugar whipped cream: Use a hand blender to whip the heavy cream and brown sugar together until you reach soft peaks so it sits nicely on top of the drink.
To make the drink: Make the espresso or coffee. In a large jar with a lid add the ice and the espresso. Add the lid and shake for 60-90 seconds. The espresso will lighten in color and become foamy on top. (Brewed coffee will lighten in color but won't foam quite as much.)
Add some extra ice to a tall glass. (I like extra ice, you can skip it if you want to.)
Pour the shaken espresso over the ice. Add 2 tablespoons of the brown sugar syrup and mix gently with a straw.
Add the oat milk and then the whipping cream. Sprinkle with cinnamon (optional) and add a straw. Serve.
Notes
No espresso? Try percolated coffee, french press, pour-over, or instant coffee instead.The syrup makes enough for 4 drinks using 2 tablespoons each.