Line bottom of 6″ round cake tin, no greasing. Preheat oven to 180 deg C.
Add hot water to cocoa powder and stir till dissolved. Add in cold milk and stir. Set aside.
Add corn starch to sugar and mix well. Set aside.
In a mixing bowl, beat egg yolks and add in salt.
Add in oil and whisk till even.
Add in cocoa mixture and whisk. Then add in sifted cake flour and mix till no dry bits.
Using a mixer, whisk egg whites till foamy then add in cream of tartar. Add in sugar and corn starch mixture in 2 parts and whisk till firm peak.
Mix 1/3 of the meringue into yolk batter with hand whisk.
Pour yolk batter into remaining meringue. Use spatula to fold till combined.
Pour slowly into cake tin and add chocolate chips on top.
Bake at 180 deg C fan forced for 10 min.
After 10 min, take out and make slits. (Below is another cake for illustration.)
Continue to bake at 180 deg but without the fan (only top and bottom heat), for another 20-25 min. Cool inverted.
Unmould and slice.
