Put the Vodka and Crème de Menthe (add as little or as much as you like depending on how minty you want it) in the bottom of your glass; the size and shape is up to you...
Then top up your glass with Lemonade and voilà! Enjoy!
You could add a slice of Lemon, Lime or a sprig of Mint for effect, if you wish. And add ice if desired!
I had this at a performance of Wicked the Musical at the Apollo Victoria, London... was very nice, and atmospheric!