This is a classic variation on the Bijou cocktail. I was introduced to this cocktail by a regular denizen at Death & Co. in Manhattan. The following comes from their book, linked below.
1 1/2 oz. Gin
1 oz. Sweet Vermouth
1 oz. Green Chartreuse
Stir together gin, vermouth, chartreuse, and bitters in a mixing glass.
Use the Campari to rinse the inside of the serving glass, discard extra.
Garnish with a twist of lemon.
Photo by Lisa Denkinger