Separate egg yolks and whites. Set aside. Keep the egg whites chilled in the fridge.
Preheat the oven to 150°C.
In a mixer bowl, add in oil and milk, whisk to combine. Sift in cake flour. Combine well.
Add in egg yolks and 15g sugar. Mix well.
In another mixer bowl, beat the egg whites to make a meringue, adding in sugar in 3 separate times. Beat until stiff peak forms.
Add ⅓ of the meringue into the egg yolk mixture, then whisk to combine. Gently fold this mixture into the remaining meringue.
Pour the batter into a 6-inch chiffon cake pan, then stir with a tooth pick or a baking needle, and tap the cake pan against the table to remove air bubbles.
Bake in the oven at 150°C for 50-55 minutes.
When it’s baked, take out the pan from the oven and let cool upside down. Unmold when the cake is completely cooled down.