The Sidecar cocktail has been in circulation for a century, and over those many decades, it’s been many things: an iconic brandy cocktail; a relic of Parisian cocktail culture from the 1920s; and even, in its early days, an equal-parts drink, composed of brandy, lemon juice, and orange liqueur. That version, for obvious reasons, didn’t stick around for long, and today’s bartenders continue to tweak the classic formula for contemporary palates. At Gage & Tollner in Brooklyn, co-owner St. John Frizell included the Sidecar on his classics-heavy cocktail list, with a minor modification: A small touch of sugar is added to each drink, to bridge the sweetness gap found in most Sidecar versions, and to give the cocktail superlative balance.