As I was walking down Rue Victor Massé in Paris’ hip South Pigalle district, an unexpected sight stopped me short: a row of giant Chartreuse jeroboams displayed in the window of wine bar 228 Litres. Later at another noted spot, L’Orillon, there it was again, the electric-green liqueur arriving at tables all around. This was the city that, some 25 years ago, put natural wine bars on the map. Today those same bars have a new obsession: a digestif made by monks for the past 300 years. “Everybody...