01 - In a cocktail shaker or sturdy glass, combine the raspberries, mint leaves, lime wedges, and simple syrup. Muddle thoroughly until the berries are crushed and release their juices, and the mint releases its aromatic oils.
02 - Pour in the white rum (if using), lemon-lime soda, and sparkling water. Stir well to incorporate all the flavors and ensure the simple syrup is fully dissolved.
03 - Place one large scoop of vanilla ice cream into each of the two tall glasses, ensuring they are chilled and ready for the liquid mixture.
04 - Strain the raspberry-mint beverage mixture evenly over the ice cream in both glasses, pouring gently to create the layered float effect.
05 - Lightly stir to marble the flavors together. Garnish each glass with fresh mint leaves and additional raspberries. Serve immediately with straws and long spoons.