(1 oz = 30 ml)
You can adjust the strength of the drink by varying the amount of vodka (0x - 2x works). You can adjust sweetness by varying the ratio of Pimm's to Cointreau, as long as the total volume of the two is 1 oz (personally, I prefer 0.33 Cointreau and 0.66 Pimm's). Also, be careful about the amount of ginger beer you top with, it's easy to get too sweet.
If you don't have bitters, you can get away with just using tea and steeping in the shaker for an extra minute. The Bengal Spice is especially good in this case. However, DO NOT try to make this drink without either tea or bitters, it's nasty! (Cathy calls it Mr. Pimm's Breakup when I forget the bitters.)
/Brian Karlak (July 2014)