Halve the passion fruit, squeeze and bring to the boil with the mango juice in a saucepan. Pour through a sieve.
Add sugar, cardamom, vanilla pulp and orange liqueur, bring to the boil again and reduce over low heat for about 5 minutes. Fill the passion fruit syrup into bottles and leave to cool for at least 2 hours. Close the bottles tightly.
Tastes good when poured with water or sparkling wine, over ice or to refine quark dishes. The syrup has a shelf life of 3 months.