Preheat the oven to 180°C and place 12 paper cases in a muffin tray.
Beat the butter and sugar in a bowl until pale and creamy.
Add the eggs one at a time and beat until well combined.
Fold the flour, raspberries, and passion fruit pulp into the mixture until nearly smooth.
Add a little milk if the mixture appears too stiff.
Divide the mixture among the cases and bake for 20 minutes.
Cool in the tin for 10 minutes then transfer to a wire rack to cool completely.
Whisk the icing sugar and butter together until light and fluffy.
Whisk in the vanilla seeds and food colouring.
Gradually whisk in milk until a smooth paste forms.
Pipe the icing over the cooled cakes with a star-shaped nozzle and top with sprinkles.