pièce de résistance

1. An outstanding accomplishment: "The bison is an evolutionary pièce de résistance, the result of thousands of years of genetic development under the toughest weather and geographical conditions" (B.J. Roche).
2. The principal dish of a meal.

[French : pièce, piece + de, of, with + résistance, staying power, lastingness.]

The noun has 2 meanings:

Meaning #1: the outstanding item (the prize piece or main exhibit) in a collection
  Synonyms: collector's item, showpiece

Meaning #2: the most important dish of a meal