Place the watermelon cubes in a blender or food processor and blend until smooth.

Add the granulated sugar, lime juice, and vanilla extract (if using) to the blender and blend again until fully combined.

Pour the watermelon mixture into a shallow, freezer-safe container and spread it out evenly.

Cover the container tightly with a lid or plastic wrap and place it in the freezer.

Freeze for 4-6 hours, stirring the mixture every 30 minutes for the first 2-3 hours to prevent ice crystals from forming.

Once fully frozen and smooth, scoop the sorbet into bowls or cones and serve immediately.