The ultrasmooth French 75 cocktail is named for an equally ultrasmooth 75-millimeter artillery cannon used in World War I. In this version, the alluring blend of gin and sparkling wine gets an aromatic herbal lift from celery-infused syrup.
Combine sugar and water in a small saucepan. Bring to a simmer over medium heat, stirring until sugar is dissolved. Remove from heat; add celery leaves. Let syrup cool. Pour through a fine sieve into a bowl; discard leaves.
To assemble each cocktail, combine 1 tablespoon celery syrup, 1 tablespoon lemon juice, and 1/2 ounce gin in a Champagne glass. Top off with wine; gently stir to combine. Garnish with celery leaf and lemon rind or twist; serve immediately.