An old Martini variant which was first published in Hugo R. Ensslin's 1917 book Recipes for Mixed Drinks with instructions to be stirred.
Half-fill a cocktail shaker with ice.
Add the dry gin and dry vermouth to the jug and stir until well-chilled.
Strain into a chilled cocktail glass and garnish with an olive.
The "fifty fifty" in the references the 50% of dry gin and %0% of dry vermouth, but we've also opted to make this with 50ml of each.