Mix 10g cocoa powder with 20g hot water until completely smooth. Set aside to cool while preparing other ingredients.

Separate 5 eggs into whites and yolks. Place the egg whites in the freezer for 20 minutes to chill.

In a bowl, combine 65g warm milk with 60g corn oil. Mix until well combined.

Sift in 75g cake flour and stir in straight lines until smooth.

Add the 5 egg yolks and mix in straight lines until the batter is completely smooth.

Remove chilled egg whites from freezer. Beat until large bubbles form.

Add 60g sugar in three parts: beat after first addition until bubbles become finer, add second portion and beat until thickens, add remaining sugar and continue beating until soft peaks form.

Fold one-third of the meringue into the yolk mixture gently.

Pour this mixture back into the remaining meringue and fold gently until completely smooth and uniform.

Scoop out 180g of the plain batter into a separate bowl.

Pour the remaining batter into a lined baking pan and spread evenly.

Mix the cooled cocoa paste with the reserved batter until smooth.

Transfer to a piping bag and cut a small tip.

Pipe lines of cocoa batter across the surface of the plain batter.

Using the back of a spoon, draw lines through the batter touching the bottom of the pan to create a pattern.

Tap the pan lightly to release air bubbles.

Preheat oven and bake at bottom heat 155°C / top heat 165°C for 20 minutes, then adjust to bake at bottom heat 155°C / top heat 170°C for another 10 minutes.

Remove from oven and tap pan to release steam. Cool at room temperature for 10 minutes.

Cover with parchment paper and flip the cake. Peel off the bottom paper.

While still warm, roll the cake parallel to the bottom pattern using a rolling pin. Wrap tightly in parchment paper and let set at room temperature for 30 minutes.

After 30 minutes, unwrap carefully. Trim the ends for a neat appearance if desired.

Slice to reveal the beautiful marble pattern inside.