1Put the sugar, water and vanilla extract in a medium saucepan. Stir over medium heat for 3-4 minutes until the sugar dissolves. Increase heat and simmer for 2 minutes. Pour the syrup into a large heatproof bowl. Allow to cool.
2Cover and refrigerate 3 hours until cold.
3Blend or process the pears and lemon juice until smooth. Strain the mixture into a bowl, pushing the mixture through the sieve. Discard the solids. Cover and refrigerate until ready to churn the sorbet.
4Stir the pear puree into the sugar syrup.
5Pour the chilled mixture into the ice cream bowl. Set the ice cream maker to the desired setting and churn.
6Once the sorbet is frozen, spoon or scoop into chilled bowls and serve or transfer to a freezer-safe container, just large enough to contain the sorbet. Freeze for 2-3 hours or overnight for firmer sorbet.
7Store sorbet in the freezer for up to 3 weeks. The sorbet will become very firm after freezing overnight, so remove from the freezer and stand at room temperature for 5-10 minutes before serving for easier scooping.