01 - Combine cubed watermelon and lime juice in a blender. Blend until completely smooth and no chunks remain.
02 - Pour the puree through a fine-mesh sieve into a pitcher to remove any fibrous bits for a silky smooth texture. This step is optional but recommended.
03 - Divide the strained watermelon puree evenly among 4 tall glasses, filling each about one-third full.
04 - Place one generous scoop of vanilla ice cream into the center of each glass, resting it on top of the watermelon puree.
05 - Slowly pour the chilled lemon-lime soda over the ice cream in each glass, allowing it to foam and create the float effect.
06 - Top with fresh mint leaves and watermelon balls or slices if desired. Serve immediately with a straw and long spoon.