1 kg(about 6 punnets) mixed berries, such as strawberries, raspberries and mulberries, to serveFor dusting:pure icing sugarZabaglione8egg yolks100 gmwhite sugar200 mldry Marsala, plus extra for brushing2gelatine sheets (titanium strength), softened in cold water300 mlthickened cream, whisked to soft peaks, refrigeratedSponge cake5eggs165 gm(¾ cup) caster sugar150 gmplain flour60 gmbutter, melted and cooled
For sponge cake, preheat oven to 180C. Whisk eggs and sugar in an electric mixer until tripled in volume (3-5 minutes). Sift over flour, fold to combine, then fold through butter. Spoon into a buttered and floured 17.5cm x 25cm cake pan and bake until cake springs back lightly when touched and a skewer inserted withdraws clean (15-20 minutes). Cool in pan for 5 minutes on a wire rack, then turn out and cool completely.
Trim top of sponge flush, then cut horizontally into thirds. From the top slice, cut a round to fit the base of a 1.5 litre plastic wrap-lined flat-based bowl and place in base. Cut another round from sponge to fit top of bowl and set aside. Cut remaining slices vertically into 3cm-wide rectangles and arrange around sides of bowl, leaving a gap between each. Halve remaining sponge rectangles diagonally to form triangles and fit into gaps with pointed ends towards the base. Brush prepared sponge lining with Marsala and set aside.
For zabaglione, place egg yolks and sugar in a heatproof bowl and whisk until thick and creamy (5-10 minutes). Place bowl over a saucepan of simmering water, then add the Marsala and whisk until mixture is very thick and holds a ribbon (10-15 minutes). Squeeze excess water from gelatine and whisk into egg mixture until dissolved. Remove from heat and place over ice, whisking occasionally until chilled (10-20 minutes), then gently fold through cream and spoon into cake-lined mould. Trim edges of sponge flush with zabaglione. Place reserved sponge round on top. Brush with Marsala, cover with plastic wrap and refrigerate until set (6 hours-overnight). Serve cake topped with berries and dusted with icing sugar.