Cut your watermelon into cubes, removing any seeds if necessary. For optimal flavor, choose a watermelon that sounds hollow when tapped and has a vibrant yellow spot where it rested on the ground while growing.
Place watermelon cubes in a blender or food processor and purée until completely smooth, about 30-45 seconds. If your blender is smaller, work in batches.
Pour the watermelon purée through a fine-mesh sieve into a large bowl, pressing gently with a spatula to remove pulp and fibers.
Stir in the sugar, lime juice, lime zest, and salt until the sugar completely dissolves. If using vodka, add it now.
Refrigerate the mixture for at least 2 hours until thoroughly chilled.
If using an ice cream maker: Pour the chilled mixture into your ice cream maker and churn according to manufacturer's instructions, usually 20-25 minutes until it reaches soft-serve consistency.
If not using an ice cream maker: Pour the mixture into a shallow freezer-safe container. Freeze for 45 minutes, then remove and whisk vigorously or blend to break up ice crystals. Repeat this process 3-4 times at 30-minute intervals.
Transfer the sorbet to an airtight container and freeze for at least 2 hours before serving. For perfect scooping, let it sit at room temperature for 5-10 minutes before serving.
Garnish with fresh mint leaves and lime wedges if desired.