For the green tea add 20 g boiling water; mix till smooth; add 30 g room temperature water; mix

Preheat oven to 160°C. Measure ingredients for cake and prepare green tea as detailed above.

Whisk 10 g castor sugar with egg yolks till dissolved.

Add corn oil. Whisk till just combined.

Add green tea. Whisk will just thoroughly mixed.

Sift cake flour into mixture. Whisk till just thoroughly mixed but small lumps are still visible.

Separately whisk egg whites till frothy. Add lemon juice. Whisk till thick foam forms.

Gradually add 45 g castor sugar whilst still whisking. Continue to whisk till firm peak stage

Add half of egg whites. Mix with whisk till almost even. Add remaining egg whites. Mix with whisk till almost even. Scrape down and fold with spatula till just evenly mixed, banging mixing bowl against worktop 2-3 times.

Pour batter into 20 x 12 x 7.5 cm cake pan, slowly and from about 30 cm high. Jiggle pan till batter is level.

Place cake pan holding batter in 23 x 15 cm cake pan. Tuck cardboard between 2 pans. Bake till middle of cake doesn't make squishing sound when pressed gently, about 55 minutes.

To make whipped cream, whisk cream till just thick enough to hold its shape. Add green tea powder. Whisk till evenly mixed and cream is dead stiff.

To assemble, cut cake horizontally with serrated knife or cake slicer into 2 equal halves. Set aside bottom half of cake. Invert top half so that cut side faces up. Spread with half of whipped cream. Top with remaining half of cake, cut side down. Spread with remaining whipped cream. Smooth top. Trim about 1 cm from 4 edges. Transfer cake to serving plate. Refrigerate till ready to serve. Enjoy trimmings whilst waiting.