Cut the passion fruit in half and scoop out the pulp into a large pan.
Add the raspberries, sugar and 250ml (8fl oz) cold water. Heat gently, stirring until the sugar has dissolved, then bring to the boil and bubble for 2 minutes.
Pass the fruit mixture through a fine sieve into a bowl or large jug that can hold up to 500ml (17fl oz).
Allow to drip through, stirring gently, but be careful not to press. Discard the pulp and seeds. Stir in the vodka (this helps to prolong the life of the syrup).
Pour the syrup into the bottles, seal tightly, label and decorate as you like.
Keep in the fridge for 3 months unopened and 1 month opened.
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