Preheat the oven to 180°C and grease a Swiss roll tin.
Cream butter and sugar until fluffy, then beat in eggs and milk for five minutes.
Mix in flour and baking powder, then fold in raspberries, passion fruit, and food coloring.
Spoon mixture into the tin and bake for 25 to 30 minutes until golden.
Beat butter and icing sugar for the frosting, then mix in coloring, vanilla, and lavender.
Transfer frosting into a piping bag fitted with a star-shaped nozzle.
Assemble cakes by layering cut sponge circles, frosting, jam, and fruit into the tubes.
Top with a final layer of frosting and decorate with sprinkles.