Preheat oven to 170C. Beat butter, sugar and rind using an electric mixer until light and fluffy, add eggs and beat to combine, then add sour cream and beat to combine. Fold in flour, then spoon mixture among 10 greased and floured 150ml-capacity dariole moulds and bake for 15 minutes or until golden. Cool for 5 minutes then turn onto a wire rack to cool completely.
For syrup, combine all ingredients and ¼ cup water in a small saucepan and stir over medium-high heat until sugar dissolves, then bring to the boil and simmer for 10 minutes or until syrupy. Makes about 1 cup.
For cream, combine ingredients and whisk until soft peaks form. Refrigerate until required.
To serve, pour half the warm syrup over cool cakes and serve with passionfruit cream and extra syrup passed separately.