To make this pretty lime twist, use a vegetable peeler to make one long peel of a lime zest. Use scissors to trim off an even, narrow strip and then twist that strip of lime skin around a chopstick. Set aside (or in the freezer) while you prepare the cocktail.
Measure your ingredients into your cocktail shaker with ice and shake vigorously for 1 minute.
Strain cocktail into a martini glass and garnish with your lime wedge or twist.
We don't recommend using plain vodka simply because citron (citrus flavored) is not only the classic ingredient for a cosmopolitan, but because it tastes better. If you have plain vodka on hand and don't want to hit the store, you can certainly use it, but grab some citron on your next store trip.