Juice of 1/4 Grapefruit (1 oz)
1 Egg White
1 liqueur glass Green Chartreuse (2 oz)
Shake once without ice and once with and strain into a cocktail glass. I strained into a rocks glass and garnished with a mint leaf.
Postnote: See the entry for the Milord Gower as to why the St. Germain acquired its name.