Preheat oven to 325°F/163°C.
Line two 6" round pans with parchment paper. Set aside.
In a bowl, whisk together egg yolks with 40g granulated sugar, oil, coconut milk, and coconut extract.
Sift in the cake flour over top of the egg yolk mixture and fold gently to combine, until there are no lumps.
In a clean stand mixer bowl fitted with a whisk attachment, add in the egg whites and mix on low speed.
Once the egg whites are slightly foamy with bubbles, add in a little cream of tartar (or lemon juice/vinegar).
Gradually increase the speed of the mixer, and slowly pour in 40g granulated sugar.
Continue to whip the egg whites until fluffy, shiny and reaches a soft peak. (The egg whites will form a curved tail at the end of the whisk).
Fold about a third of the egg whites into the egg yolk batter.
This will help to loosen up the egg yolk batter.
Add the next 3rd of the egg white mixture, folding it into the egg yolk mixture.
Continue to fold until all of the remaining egg white mixture is incorporated into the batter, taking care not to overfold.
Divide and transfer the cake batter into two 6" round pans (use a scale to evenly distribute).
Gently tap the pans a few times to release any trapped air bubbles.
Bake at 325°F/163°C for 25-30 minutes, or until a toothpick inserted comes out clean.
Remove the cakes from the oven and carefully drop them on the counter from a height of about 1' (to prevent too much shrinkage).
Cool the cakes in the pan for about 2 minutes before transferring to a wire rack to cool completely.