Put the brown sugar syrup ingredients into a pan. Heat it with medium heat and bring it to boil. Turn the heat to low. Continue stir and let it simmer for 3 mins. Put it aside
Making the shaken espresso
Combine the espresso and brown sugar. Add them and ice into the shaker. Shake for 15 seconds
Pour the mixture in a tall glass and fill half of it. Add the oat milk. Mix it well and serve.
Notes
The espresso I used1 The brown syrup can make 4-6 cup. It can prepare in advance and store it in the fridge2 If you don't have espresso maker, you can use the instant coffee with stronger taste. Put 1-2 tsp of it and dissolve it in 50ml cold water