The Collaborative International Dictionary of English v.0.48:

Bercy \Ber"cy\ n.
   a sauce prepared from butter creamed with white wine,
   shallots, parsley and fish stock; -- also called Bercy
   sauce.

   Syn: Bercy butter.
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

Bercy
    n 1: butter creamed with white wine and shallots and parsley
         [syn: Bercy, Bercy butter]