To follow this cocktail's original proportions use 60ml (2oz) dry gin and omit the Old Tom, but you'll be missing out. Either way, despite the rich liqueur...
I made this with St. George Valley gin (didn't have any Old Tom) and Cinzano. I felt like I couldn't quite get the taste right; I tinkered with amounts of lemon, Grand Marnier, and finally added a bit more gin and that seemed to do the trick. Next time I'll lean a little heavier on the gin in the beginning.
I had no Old Tom so I made this with 2 oz Bombay Sapphire. I also added 1/4 oz of simple to dial the dryness down just a bit, and ended up quite liking it. The lemon comes through nicely, and it benefits from using Grand Marnier instead of Cointreau/triple sec.
Not a favorite. Doesn’t much taste like a Martini, but it certainly is dry despite the Cointreau and sweet vermouth. Also used Ransom Old Tom (which is not sweet, despite the name).
Could use a little more roundness. Contrary to Simon’s tip, I actually liked it a bit more as it warmed up a tad.