Cut the watermelon in half lengthwise and scoop out the flesh using a spoon or melon baller. Reserve the flesh to extract juice or enjoy separately.

Blend the watermelon flesh and strain through a fine mesh sieve to collect 1 cup of juice. Discard the pulp.

In a small saucepan, combine 1 cup watermelon juice, lime juice, and sugar (if using). Heat over medium-low heat until warm but not boiling.

Sprinkle the unflavored gelatin over the warm mixture and whisk continuously until the gelatin is fully dissolved, about 2-3 minutes.

Remove the saucepan from heat and stir in the vodka until fully combined.

Carefully pour the mixture into the hollowed-out watermelon halves, dividing evenly.

Refrigerate the watermelon halves for 3-4 hours, or until the jello has fully set.

Once set, slice the watermelon halves into small wedges or triangles for serving.

Garnish with fresh mint leaves if desired and serve chilled.