• 300g caster sugar
• 1 cup water
• 4 eggwhites
• 1 tsp cream of tartar
• 500g unsalted butter, chopped, softened
• 2 tsp vanilla bean paste
• 1 cup passionfruit pulp, sieved
• 2 x 16cm sponge cakes
• 1 cup orange liqueur or juice
• Passionfruit pulp, to drizzle
Put sugar and water in a saucepan and bring to the boil over a high heat, occasionally brushing down sides of pan with a damp pastry brush. Cook until sugar syrup has reached ‘soft ball’ stage (see the handy tip below) or 115°C on a cook’s thermometer.
Cooks' tip: Sugar syrup has reached ‘soft ball’ stage when 1 tsp of it added to a glass of ice-cold water becomes a soft and sticky solidified ball once removed.
Meanwhile, put eggwhites and cream of tartar in the bowl of an electric mixer and beat on medium using whisk attachment until soft peaks form. With motor running, add hot sugar syrup in a slow steady stream, beating until cool. Transfer meringue mixture to a large mixing bowl and set aside.
Put butter and vanilla in second bowl of an electric mixer and beat on medium for 5 minutes or until very light. Add passionfruit in a slow stream, beating until smooth and light.
Fold passionfruit mixture into meringue mixture until combined. Divide frosting in half, setting 1 half aside.
Using a serrated knife, slice both cakes in half horizontally. Put 1 half on a cake stand, cut-side up. Drizzle with a little of the orange liqueur or juice, then top with a thick layer of frosting. Repeat with remaining cake halves, liqueur, then frosting, finishing with liqueur.
Spread reserved frosting around sides and top of cake until smooth. Chill in fridge for 15 minutes.
Drizzle cake with extra passionfruit. Serve immediately.