1.Preheat oven to 180°C/350°F. Grease and lightly flour a 24cm bundt pan (see tip).
2.Strain passionfruit over a medium jug; reserve juice for cake mixture, and seeds for lemon syrup.
3.Beat butter, rind and sugar in a small bowl with an electric mixer until light and fluffy. Beat in eggs, one at a time. Transfer mixture to a large bowl; fold in combined buttermilk and reserved passionfruit juice, and the sifted flour in two batches. Spread mixture
4.Bake cake for 1 hour or until a skewer inserted into the centre comes out clean. Leave cake in pan for 5 minutes before turning onto a wire rack placed over a tray.
5.Meanwhile, make lemon syrup. Place sugar, lemon juice, the water and half the reserved passionfruit seeds (discard remaining seeds or freeze for another use) in a small saucepan; stir over heat, without boiling, until sugar dissolves. Simmer, uncovered, without stirring, for 5 minutes.
6.Pour hot syrup over hot cake; serve cake warm.
You will need about nine passionfruit for this recipe.
You can also make the cake in a greased and lined deep 22cm (9in) round cake pan or a buttered and floured 21cm (8½in) baba cake pan.