Note that this is a gin based cocktail. If you want to make a vodka and dry vermoth that's fine with me, just don't call it a martini.
2 oz gin (Hendriks, North Shore 11, The Botanist)
¾ oz dry vermouth (Dolin, Noilly Pratt)
2 dashes orange bitters (Regans or Angostura*)
lemon twist or olive by choice
Add the bitters, vermouth, and gin to a rocks/old-fashioned glass. Fill glass with ice stir (do not shake!). If you are serving it "up", strain it into a Martini/Cocktail glass, or if it's to be "on the rocks" leave it where it is. Drop in the twist or olive and serve.
Note that this a "classic" recipie, with a less than 3:1 gin to vermouth ratio. 4:1 or even 5:1 seems to be a bit more common these days, but l further than that and I would just pour gin over ice and call it done. This bit of theater with adding a few drops of vermouth in a glass of gin is just snobbery, IMHO.
* Yes, Angostura makes a very nice orange bitters if you can find it.