It's the Improved Holland Gin Cocktail. My nr1 favorite: 2shots Bols Genever, 1/4shot Bols Maraschino, 1barspoon sugar sirop, 2sprays Absinthe and 2bits of Angostura Bitters. Fill a shaker with ice, and all ingredients, stir and strain through a Hawthorn strainer in a chilled martini glass, squeeze a citrus peel and rub the edges of the glass with it before dropping it in the drink. Heaven!