Add ingredients to a cocktail shaker filled with hard cracked ice and strain into a chilled glass. The exact proportions will differ depending on the quality and intensity of the Cognac being used—one of the kosher X.O.s would be my choice, like the Godet X.O., the Dupuy X.O., or the Louis Royer X.O.—in the past it would have been made with a V.S.O.P., but for contemporary Cognac production, an X.O. will give better results.
I should also note that this one is strictly for home use. First, no bar carries kosher Cognac. Far more importantly, however, even if they did they’d probably mess it up because this requires fine-tuning to personal taste to get just the right balance. It won’t take long to tinker, and the results will be very well worth the effort.