There was a silly memory game I played while in bartending school to remember nuances about certain drinks. I'm rather embarrassed to admit that in this case, Debbie Gibson singing ‘Shake Your Love’ pops in my head. I’m sure she digs onions.
Serve on the rocks or in a chilled stemmed glass, I prefer the latter. In your shaker add ice, as few or many drops of Dry Vermouth for your taste, 2 ounces Vodka or Gin (latter wins again), shake your love, pour in glass, add cocktail onions for garnish.
We many never know the true origin of this cocktail as there are a few versions floating around. My favorite is of an American banker named Gibson who would take his clients out for business lunches. He would have the bartender serve him cold water, permitting him to remain sober while his clients, not so much. The onion garnish served to distinguish his beverage from those of his clients.