Pour gin, limoncello, lemon juice, and simple syrup into a shaker with ice. Shake for about 10 seconds.
Strain into a chilled champagne flute.
Top slowly with chilled champagne, prosecco, or cava.
Stir gently with a bar spoon to blend, keeping the bubbles lively.
Garnish with a lemon twist.
Notes
Use dry gin for balance, or swap for vodka for a softer profile. Prosecco offers a fruitier twist, cava a drier finish. Chill glassware before serving to preserve bubbles.