The sidecar is a straightforward concoction, consisting of equal parts cognac or brandy, lemon juice, and Cointreau. Like most cocktails, it has an obscure history, but it is one of the many cocktails to emerge after the first world war. It can also be prepared with two parts cognac, one part lemon juice, and one part Cointreau; this is how it's done in the 1930 Savoy cocktail book. It's usually served with a lemon twist or a sugared rim. I recommend adapting the Sidecar to suit your tastes, because it is a such a lovely, simple drink. That said, this is how we prepare them:
Sidecars, for Two Aesthetes
2 ounces brandy
(or cognac)
2 ounces Cointreau
2 ounces fresh lemon juice
1/2 teaspoon sugar
(optional)
Combine lemon juice and sugar, if desired, and pour into a cocktail shaker. Add the brandy or cognac and Cointreau. Shake vigorously with ice, and pour into cocktail glasses. Serve with a lemon twist.