2 1/2 ounces gin
1/2 ounce dry vermouth
1 dash orange bitters (optional)
Garnish: Lemon twist, or a green olive
Stir with ice. Strain into a cocktail glass.
This is a 5-1 ratio Martini. An "extra-dry" martini can take this to such an extreme as to have no vermouth at all. Which sort of missses the entire point of what a cocktail (much less a Martini) is all about.

While I much prefer more vermouth in my Martini than is used here, I think this version provides the "dryness" that most drinkers expect from a gin Martini and yet still gives them a little bit of culinary interest from the vermouth. So while I typically wouldn't recommend serving a 3-to-1 Martini to a random customer who just asks for a (gin) Martini, I think this version would work well for that and begins to provide the customer a little bit of insight as to what they might be typically missing in a Martini