In a large bowl add the butter, icing sugar and vanilla and mix until it is all combined.
Split the mixture evenly between two bowls.
In one bowl add a teaspoon of Prosecco one at a time and mix between each addition until the buttercream reaches the desired consistency.
Add a small amount of pink food colouring to the Prosecco buttercream and mix. Keep adding small amounts until you reach the desired consistency. Leave to one side.
Put a seive over a small bowl and cut the passionfruit in half and remove the seeds into the sieve. The juice should drain into the bowl.
With your second bowl of buttercream add 1tsp of Passionfruit one at a time until it reaches the desired consistnecy. The passionfruit juice should make it a lovely yellow colour but you could add a little yellow food colouring to enhance the colour.
Cut a strip of cling film and lay it down on your work surface, genlty spread the pink buttercream along the clingfilm. Spread the yellow buttercream beside it.
Roll the cling film up and tie off both ends.
Cut one of the ends and put the clingfilm into your piping bag.
Pipe the buttercream onto the top of the cake and finish with some sprinkles.