Pre-heat your oven to 160C Fan/180C/350F/Gas Mark 4, and grease and line three 8" cake tins (that are at least 2" deep)
Make the sponge by mixing the butter and caster sugar in a large bowl, ideally with an electric mixer, until fluffy and pale - about 3 minutes
Add the eggs and vanilla extract, and whisk until fully incorporated
Add the self raising flour and whisk in gently until you can't see any flour anymore. Then fold in the lime zest
Divide the mixture between the tins, use scales for accuracy
Bake them for 35-40 minutes or until a skewer inserted in the middle comes out clean. Leave them to fully cool either in the tins or on cooling racks
While they are baking, mix the lime juice and sugar together for the syrup, stir it occasionally, the sugar will dissolve eventually
If the cakes have domed on top, level them off with a cake leveller or a serrated knife
Poke the cakes all over with a thin skewer, then brush the syrup evenly over them
To make the buttercream, mix together the butter and icing sugar, this is best done using an electric mixer
When it starts to come together add the prosecco (or prosecco flavouring and milk if using), and whisk until smooth
Stack the sponges up on your plate or cake stand, piping or spreading buttercream between each layer. Drizzle the passion fruit curd over each layer of buttercream
When you get to the last layer, pipe larger rosettes all around the edge and smaller ones in the centre, drizzle over more passion fruit curd and add some fresh passion fruit and sprinkles too, if you like
Serve immediately, store leftovers in an airtight container in a cool place and eat within 3 days