Which cocktail contains Aperol as a key ingredient?

The cocktail that contains Aperol as a key ingredient is the Aperol Spritz. This refreshing drink is a popular Italian cocktail that highlights the unique flavors of Aperol, an aperitif characterized by its orange hue and bittersweet taste. The Aperol Spritz is typically made by combining Aperol with Prosecco and a splash of soda water, resulting in a vibrant and effervescent drink perfect for warm weather or social gatherings.

In the other cocktails listed, Aperol is not a component. The Old Fashioned, for instance, is a classic whiskey-based cocktail made with bourbon or rye, sugar, and bitters, while the Negroni is traditionally crafted with gin, vermouth, and Campari. The Mojito, on the other hand, is a refreshing blend of rum, mint, lime juice, sugar, and soda water, highlighting a completely different flavor profile. Therefore, the Aperol Spritz stands out as the correct choice due to its essential use of Aperol, making it a signature cocktail of that particular liqueur.