Which ingredient is commonly found on the top of a buffalo chicken sandwich?

The ingredient that is commonly found on the top of a buffalo chicken sandwich is hot sauce. This is a key component that defines the flavor profile of buffalo chicken, providing the signature spicy and tangy taste that characterizes this popular dish. The hot sauce, often a type like Frank's RedHot, is typically combined with butter before being applied to the chicken, but it is most recognizable as the topping that signifies the buffalo style.

Shredded mozzarella, ranch dressing, and red pepper flakes can all be associated with buffalo chicken sandwiches but do not serve as the traditional topping. Shredded mozzarella is more commonly used in other types of sandwiches and pizzas. Ranch dressing is often served as a dipping sauce on the side or drizzled on the sandwich rather than as a topping underneath the hot sauce itself. Red pepper flakes may be used to enhance flavor but are not a standard topping on buffalo chicken sandwiches like hot sauce.