- Peel 4 long, thin curls of zest from the lime with the large channel blade on the side of a bar zester. Put the sugar cubes on a saucer and sprinkle them with droplets of bitters until they are saturated but not falling apart. Put a sugar cube in each of 4 champagne flutes.
- Add a jigger of cognac to each flute and fill it with champagne. Garnish with lime zest, either hanging on the rim or floating in the cocktail, and serve at once.