Steam and froth the milk and oil so it’s hot and foamy. If your espresso machine has a frothing wand, you can use that, or you can use a milk frother or even do this with a whisk by hand on the stovetop.
Pour the hot milk and foam on top of the espresso.
Notes
You can use dairy milk or a milk alternative like oat milk. Starbucks uses Partanna olive oil but any high-quality, mild-flavored olive oil can work well. If you’d like to sweeten, this you can; I’d recommend a teaspoon or more simple syrup.