Gin & Tonic. If you can say it, you can make it. Right? Not exactly. The two-ingredient cocktail, which got its start in the 19th century as an antimalarial for British soldiers, requires your undivided attention. From glassware to garnish to spirit proof—45% ABV and above, if you mean business—everything should be carefully considered when mixing a G&T. But perhaps the most important variable is the ratio. A Gin & Tonic made with two-parts tonic to one-part gin is a highball of balance and beauty. Easy. Right?