Final answer:
When a customer wants a blonde espresso shot, you would mark the cup with an abbreviation such as 'BL' to indicate their preference for a blonde espresso roast.
Step-by-step explanation:
If a customer requests a blonde espresso shot, you would mark the cup accordingly to indicate their preference for this specific type of espresso roast. While the question does not specify the exact marking system, typically, a barista would make a notation such as 'BL' or another predefined indicator that the establishment uses to denote blonde espresso. This is similar to measuring ingredients for a coffee maker; precise execution ensures the desired outcome, much like following a recipe. In the context of making an espresso, this means selecting the right type of coffee roast as per the customer's request.