Pièce de résistance
From The Art and Popular Culture Encyclopedia
Pièce de résistance is a French term (circa 1839), translated into English literally as "piece of resistance", referring to the best part or feature of something (as in a meal), a showpiece, or highlight. It can be thought of as the portion of a creation which defies (i.e. "resists") orthodox or common conventions and practices, thereby making the whole of the creation unique and special. The phrase gives the sense that the referred-to element is the most outstanding, notable, or defining of the collection.
Originally, the pièce de résistance was the most substantial dish in a meal, but now the term generally refers to quality, not quantity.