2 spg Mint
1⁄2 oz Sweet vermouth
1⁄2 oz Dry vermouth
2 oz Gin
Muddle one of the sprigs and vermouths in a mixing glass. Add the gin and ice, stir well and strain into a martini glass. Garnish with the remaining mint sprig.
The Savoy book has this as 1/3 each dry gin, Italian and French Vermouth shaken and strained into a cocktail glass with a mint sprig garnish.