Preheat your oven to 170C/150 Fan, and line two 8"/20cm cake tins with baking parchment.
In a stand mixer, or a large bowl, beat together the unsalted butter and caster sugar until light and fluffy.
Add in the eggs, self raising flour, and vanilla and beat again until combined well.
Split the mixture between the two tins.
Bake the cakes in the oven for 50-60 minutes, or until baked through - check with a skewer to make sure they're done!
Leave the cakes to cool in the tins for 10 minutes, and then take out and leave to cool fully on a wire rack!.
Syrup
Add the passionfruit liqueur, prosecco and caster sugar to a pan.
Heat on a low heat and stir to dissolve the caster sugar
Turn the heat up high and reduce the liquid until it thickens, is syrup like, and reduced by half.
Once your cakes have cooled, split each cake into two so you have four layers in total.
Drizzle the reduced syrup over the sponges, leaving enough for the buttercream later.
Buttercream
Beat the unsalted butter on its own for minute or two, to soften it and loosen it.
Add in the icing sugar and beat well until smooth and fluffy.
Add in the cooled syrup from above and mix. Add a little food colouring at a time and beat until you reach the colour that you are after.
Decoration
Put the first cake onto a cake board of plate. Add a little buttercream and spread, and spread some passionfruit curd into the middle. Repeat with the second and third sponges. Add the final sponge on top.
Using a small amount of buttercream, spread and smooth around the cake sides and top for a crumb coat and add to the fridge for at least 30 minutes.
Once set, add more buttercream onto the tops and sides of the cake, and smooth around covering the cake completely in buttercream.
I add the buttercream on using a small angled spatula, and smoothed around the edge with the large metal scraper! You need to make sure there is more buttercream on the sides of the cake than you need, as some will be removed as you smooth it over.
Add the white chocolate and double cream to a bowl/jug, and microwave until smooth. Add white food colouring if you want to and stir.
Using a small piping bag or a teaspoon, drip the ganache down the sides of the cake. The more you push over the edge, the further the drip will fall.
Pipe any leftover buttercream onto the cake to decorate and decorate with passionfruit, sprinkles etc!
Notes
This cake will last for 3+ days.
The cake will freeze for 3+ months if wrapped well to protect it in the freezer.
Lemon curd works well if you can't buy passionfruit curd