Chill a cocktail glass by placing it in the freezer or filling it with ice water while you prepare the drink.
In a cocktail shaker, combine the light rum, raspberry liqueur, fresh lime juice, and simple syrup.
Fill the shaker with crushed ice, ensuring the ingredients are well-covered.
Secure the lid on the shaker and shake vigorously for about 15 seconds until well chilled.
Discard the ice from the chilled cocktail glass. Using a fine mesh strainer, strain the mixture into the glass to ensure a smooth pour.
Garnish with a few fresh raspberries and a lime wheel on the rim of the glass.
Enjoy your Knickerbocker cocktail immediately while it's cold and refreshing.
Notes
The Knickerbocker cocktail can be adapted by using different fruits or liqueurs based on seasonal availability or personal preference. For a twist, try adding a splash of soda water for a fizzier version.