As covered by Playboy: http://playboysfw.kinja.com/a-simple-fix-perfect-the-classic-sidecar-with-a-sweet-1517043311?linkId=8944230
1 1/2 oz. Pierre Ferrand 1840 cognac
3/4 oz. Cointreau
3/4 oz. freshly squeezed lemon juice
1 tsp. rich simple syrup*
Combine ingredients with ice in a cocktail shaker and shake until well chilled. Strain into a chilled cocktail glass. Garnish with an orange or lemon twist.
*Rich simple syrup: Combine one-half pound of sugar with one-quarter pound of water—given the different densities of sugar and water, we always do this by weight and not volume—and heat slowly while stirring from time to time until the sugar is dissolved.