Combine the butter, sugar and vanilla extract in the bowl of an electric mixer fitted with a paddle attachment and beat until pale and creamy.
To make the passionfruit syrup, combine the passionfruit pulp, water and sugar in a saucepan over a medium heat. Bring to the boil and then reduce heat to low and cook for 10 to 15 minutes. Set aside while you make the cake.
Preheat the oven to 160 degrees Celsius (320 Fahrenheit) and lightly grease a 24cm bundt tin.