Add blue curaçao, gin or vodka, lemon juice, and simple syrup.
Shake well for about 10–15 seconds until chilled.
Strain into a highball glass filled with fresh ice.
Top with soda water or club soda.
Stir gently with a bar spoon to combine without losing fizz.
Garnish with a lemon wheel or twist.
Notes
Adjust sweetness with more or less simple syrup. Increase lemon juice for stronger citrus flavor. Soda water gives a cleaner taste, club soda adds a slight mineral note. For a sweeter version, replace soda water with lemonade.