Make the meringue. Gradually add the sugar (60 g) to the egg whites and whip with a whisk until stiff peaks form.
In a separate bowl, add the sugar to the egg yolk and stir until white and frothy. Add the buttermilk and vegetable oil in that order and mix well with each addition.
Add the sifted flour into the bowl from Step 2 in one turn. Use a rubber spatula to combine well.
Add 1/3 of the meringue from Step 1 into the bowl from Step 3 and use a whisk to combine (mixing so that the batter becomes even in texture).
Add the rest of the meringue. Switch to a rubber spatula to mix the batter in cutting motions.
Pour Step 5 into the cake pan and bake for 40 minutes in a preheated 170℃ oven (the baking time varies by oven).
Once done, flip the cake pan upside down and let it cool (it's best to place it on top of a beer bottle or something similar).
Your fluffy chiffon cake is done.
Story Behind this Recipe
I had some leftover buttermilk in the refrigerator, so I thought that I could use it to make a buttermilk chiffon cake. It came out successful. The cake came out very fluffy.
It's basically the same procedure as baking a plain chiffon. As for hints, just make sure to whip the meringue until stiff peaks form and I don't think anything will go wrong. Don't forget to sift the flour. You can use plain yogurt instead of buttermilk.