Which ingredient must be included in the Shaken Espresso according to the preparation method?

The inclusion of 2% milk in the Shaken Espresso preparation method is essential because it contributes to the overall texture and flavor profile of the beverage. The fat content in 2% milk offers a creaminess that balances the robust flavor of the espresso without overpowering it, creating a smooth and enjoyable drink. This ingredient also helps to dilute the intensity of the espresso, making it more palatable while still maintaining the characteristic strength of the coffee.

In contrast to other ingredients, the use of 2% milk aligns with standard practices for shaping the classic Shaken Espresso, adding creaminess and richness. Each of the other ingredients listed may enhance or alter the drink, but they are not fundamental to the traditional preparation of Shaken Espresso.