Fill a cocktail shaker halfway with ice. Add vodka, blue curaçao, and cranberry juice.
Shake hard for about 10 seconds until the shaker feels frosty.
Strain into a chilled champagne flute or coupe glass.
Top with sparkling wine or champagne. Garnish with a lemon twist or cherry and serve immediately.
Notes
Pour the sparkling wine slowly to preserve bubbles. Use a drier brut to keep the drink from getting too sweet; add a touch more cranberry juice if you prefer deeper color and tartness.