Add 1/2 of the granulated sugar to the egg yolks, and mix until the mixture is smooth. Add the oil and water, and mix some more.
Add the sifted cake flour and baking powder, and mix until the mixture is no longer floury.
Add the remaining granulated sugar into the egg whites, and mix until stiff peaks form. It should be firm enough that if you flip the bowl, the meringue doesn't slide off.
Add 1/3 of the meringue to Step 2, and mix with a whisk to thin the batter.
Switch to a spatula, and add 1/2 of the remaining meringue, and fold it in quickly. When there are still white lumps in the mixture, add the remaining meringue, and fold it in quickly until no longer lumpy.
Pour the mixture into the mold from a height, and tap on the table a few times to smoothen the batter.
Bake in the oven preheated to 170℃ for 30 minutes. When baked, place it on a bottle or something to hold it upside down, and wait until it has completely cooled.
Run a chiffon knife around the edges of the pan to remove from the mold, and it's done.
I baked one cake in 12 cm square mold illustrated in the picture (35 minutes for baking) and one in 12 cm diameter paper chiffon mold.
When you are using 15 cm diameter chiffon mold, fill it up about 70% full and bake. You will have some leftover batter.
Story Behind this Recipe
I finally settled on this recipe. I modified the amount of the ingredients so that you won't fail and you can get the same result every time.
Bring the ingredients to room temperature. The baking time and temperature are just suggestions. The key is to work quickly and carefully. Weigh the ingredients precisely in advance.