What special feature distinguishes the Big Mac?

The distinguishing feature of the Big Mac is that it is made with three pieces of bread. This unique construction is what sets the Big Mac apart from many other burgers on the menu. The three-piece bun - consisting of a sesame seed top bun, a middle bun (known as the club layer), and a sesame seed bottom bun - allows for the addition of more toppings and flavors, creating a multi-layered experience. This design enhances the overall taste and texture, making it a signature item in the McDonald's lineup.

While special sauces and specific ingredients may add to the appeal, it is the three-piece bread structure that is specifically characteristic of the Big Mac. Other choices may refer to elements present in some versions of the burger or vary among different menu items, but the three pieces of bread are a defining trait of this iconic sandwich.