Add cognac, bitters and sugar cube (white) into a chilled champagne glass. Top up with champagne. Garnish with orange.
The first recipe citation for a Champagne cocktail goes back the "The Bar-Tenders Guide" written by Jerry Thomas in 1862. Thomas' 1862 book calls for shaking the ingredients, including the sparkling wine, which was surely a mistake since shaking carbonated drinks can get explosive.