What is the main ingredient in a Tall iced tiramisu latte?

The main ingredient in a Tall iced tiramisu latte is indeed one shot of espresso. This element is essential because it provides the foundational coffee flavor that defines the drink. The espresso contributes to the overall taste and determines the drink’s strength and richness. In a typical preparation for this drink, the espresso is combined with milk and flavored syrups, but without the espresso, the beverage would lack its primary coffee essence.

The other options focus on the flavoring and do not serve as the primary ingredient. For example, while higher amounts of espresso or flavored pumps could alter the drink's taste, the espresso is the core component necessary for an iced tiramisu latte. Therefore, one shot of espresso is crucial for ensuring that the drink maintains its identity as a coffee beverage within the Starbucks menu offerings.