Preheat the oven to 180°c and line the baking pan with parchment paper.
In a separate bowl whisk the egg white until little foamy then add salt, sugar, and whisk until a stiff peak form using an electric mixer.
Add egg yolk, one by one, and beat until fully incorporated.
Shit flour and cocoa powder in a bowl, add in two batches, and mix with a spatula until smooth.
Mix some cake mixture in oil and milk and mix in the cake batter.
Pour into the baking pan, tap the pan on a surface a few times to get rid of big air bubbles.Bake for 20 mins or until done.
Tap the pan on the surface for a few times after out of the oven while hot, remove from the pan and let it cool on a rack.