1 pint vanilla ice cream
1 1/2 cups fresh watermelon juice (see Cook's Note)
1/2 cup vodka
3/4 cup club soda
To make the watermelon juice, puree watermelon cubes in a blender until they are liquid. Strain the mixture over a mesh sieve into a measuring cup. The amount of watermelon you need will differ depending on the water content of the fruit, but a baby seedless watermelon will yield a few cups.