Brew the espresso shots and let them sit for 30 seconds to cool slightly.
Add the hot espresso, simple syrup, and vanilla extract if using to a cocktail shaker along with 1/2 cup of ice cubes.
Seal the shaker and shake vigorously for 15 to 20 seconds until the mixture is frothy and well-chilled.
Fill a tall glass with the remaining 1/2 cup of ice cubes.
Strain the shaken espresso over the ice, leaving behind the ice from the shaker.
Top with milk, pouring gently to create a layered effect, and serve immediately.