“Welcome to the turn of the 20th century,” said my guide, Marielle Chopin-Pascaud, as I entered the tasting room of Bache-Gabrielsen, on a quiet street in downtown Cognac. As four generations of Bache-Gabrielsens stared down at me from black-and-white portraits, I sipped the double-distilled brandy that bears the name of this city and region. Blended fr…