Chill a cocktail coupe or martini glass in the freezer or with ice water.
Add 45ml white rum, 30ml banana liqueur, 30ml fresh lime juice, and 5ml simple syrup into a cocktail shaker.
Fill the shaker with ice cubes.
Shake vigorously for 10–12 seconds until well chilled.
Double-strain through a fine mesh strainer into the chilled glass.
Garnish with a fresh banana slice or lime wheel on the rim.
The lime juice quantity has been corrected to 30ml - 45ml would overwhelm the banana liqueur and throw the sweet-sour balance off. A champagne flute is impractical for a shaken-and-strained daiquiri; a coupe is the proper serve and allows the aroma to open up.
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