Select and prepare the watermelon. Choose a ripe, sweet watermelon with deep color and a hollow sound when tapped. Cut into cubes, removing all seeds and rind.
Blend until smooth. Place watermelon cubes in a blender or food processor and puree until completely smooth, working in batches if necessary.
Strain the puree. Pour the puree through a fine-mesh sieve into a large bowl, pressing gently with a spatula to extract juice while leaving solids behind. This ensures a silky-smooth texture.
Add remaining ingredients. Stir in sugar, lime juice, corn syrup, and salt until completely dissolved. Add vodka if using. Taste and adjust sweetness if needed.
Chill the mixture thoroughly. Cover and refrigerate for at least 2 hours until very cold. This pre-chilling step is crucial for the best texture.
Freeze according to your preference. Either pour into an ice cream maker and churn according to manufacturer’s instructions (about 20-25 minutes), or pour into a shallow freezer-safe container for the no-churn method.
For no-churn method: Stir frequently. If not using an ice cream maker, place mixture in freezer and stir vigorously with a fork every 30 minutes for the first 3 hours to break up ice crystals.
Allow to set. Transfer churned sorbet to an airtight container and freeze for at least 2 hours until firm enough to scoop.
Let soften briefly before serving. Remove from freezer about 5 minutes before scooping for the perfect consistency. Garnish with mint leaves or lime zest if desired.