Sicilian watermelon pudding is an easy dessert with a silky texture and fresh, fruity flavor. It's the perfect, just-sweet-enough ending for hearty, heavy meals.
Puree the watermelon in a stand mixer until smooth (you can also use a hand mixer to do this in batches). Pour through a fine-mesh strainer into a measuring cup, discarding remaining solids. You should have just about 3 cups (750 ml) watermelon juice.
Ladle 2 tbsp (30 ml) watermelon juice into a small bowl and stir in the cornstarch, until smooth.
Pour the remaining watermelon juice into a medium saucepan. Bring to a boil, then simmer for 5 minutes. Add the sugar and vanilla seeds, and whisk until the sugar is dissolved. Stir the cornstarch mixture again, then whisk into the watermelon juice. Simmer, whisking occasionally, for 3 minutes, then whisk in the lemon juice.