Preheat oven to 180C/350F. Grease a 20cm x 30cm (8 inch x 12 inch) lamington pan, then line the base with baking paper.
Beat all ingredients, with exception of the icing sugar, in a small bowl with an electric mixer on low speed until combined. Increase speed to medium; beat until mixture is smooth and paler in colour. Spread mixture into pan.
Bake cake for 30 minutes. Transfer, top-side up, to a wire rack to cool.
Make passionfruit cream. Beat cream and sugar in a small bowl with an electric mixer until soft peaks form; fold in passionfruit pulp.
Split cooled sponge in half; sandwich with passionfruit cream. Serve dusted with sifted icing sugar.