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1
For the passionfruit curd, combine all ingredients in a medium heatproof bowl over a medium saucepan of simmering water. Stir constantly, until the mixture thickens slightly and coats the back of a spoon. Remove from the heat and cover the surface with plastic wrap. Refrigerate the curd until cold.
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2
For the white chocolate collar, combine the wafers and oil in a heatproof bowl over a saucepan of simmering water. Stir until melted. Cut three strips of parchment paper, 4 x 18 inches, 3 1/2 x 18 inches, and 3 x 18 inches. Spread the chocolate over paper strips on a work surface to completely cover the strips. Next, carefully lift the strips onto a clean work surface and set aside until almost firm. Score crosswise into 1 1/2 inch-wide strips. Let stand until firm. Re-cut or snap carefully into the strips. Set aside.
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3
Preheat the oven to 400u00b0F. Grease and flour two 8-inch square cake pans.
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4
For the spongecake, beat the eggs and sugar in a small bowl with an electric mixer until thick and creamy, for about 7 mins. For the initial beating, use a small bowl for maximum volume. To test if the mixture is ready, turn off the mixer, lift up the beaters and the mixture should form thick ribbons. Transfer the mixture to a large bowl.
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5
Sift the dry ingredients together twice onto parchment paper. Sift the flour mixture a third time evenly over the surface of the egg mixture. Using a balloon whisk or large metal spoon, quickly and lightly fold the flour mixture into the egg mixture until just incorporated.
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6
Divide the batter evenly among the prepared pans. Tilt the pans to spread the batter to the edge. Bake for 18-20 mins or until the sponges spring back when touched lightly in the center. Immediately invert onto wire racks and cool completely.
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7
Split the sponges in half horizontally. Sandwich both sponges with the passionfruit curd.
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8
Beat the cream and vanilla extract in a medium bowl with an electric mixer until firm peaks form. Place one sponge onto a serving plate. Spread with a 1/3 of the whipped cream and top with the remaining sponge.
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9
For the passionfruit icing, sift the powdered sugar into a medium heatproof bowl. Stir in the passionfruit pulp and water. Stir the icing, over a saucepan of simmering water until spreadable.
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10
Quickly spread the passionfruit icing over the top of the cake. Spread the sides of the cake with the remaining whipped cream. Press the white chocolate strips around the sides of the cake. Tie with ribbon to secure. Top the cake with flowers, if desired.
