Cognac is a brandy of French origin.
Cognac was illegal on Terok Nor during the Occupation of Bajor, although Quark kept a bottle underneath his bar area. (ST - Terok Nor novel: Dawn of the Eagles)
In 2372, Joseph Sisko wanted to open a bottle of cognac when Benjamin Sisko returned home. (DS9 episode: "Homefront")
In 2376, Quark served Cognac at a reception for Federation, Bajoran and Cardassian delegates on Deep Space 9. (DS9 - Mission Gamma novel: This Gray Spirit)