To make a Pandan Chiffon Cake, first put the egg yolks and sugar into a mixing bowl and mix them for about 4-5 minutes until the mixture turns lighter. Add vegetable oil and continue beating. Then, add coconut milk and pandan paste; the color will change to light green. Gradually add the sifted cake flour and mix until just combined, then set the mixture aside.
Wipe another mixing bowl and whisk with white vinegar to ensure it is clean. Whisk the egg whites at low speed until foamy for about 1-2 minutes. Add cream of tartar and continue whisking, gradually adding sugar to the egg whites. Increase to high speed and keep whisking until the egg whites form a stiff peak, which takes around 5-7 minutes. Be patient.
Gently fold a third of the meringue into the green yolk mixture, then fold in the remaining meringue in two batches until thoroughly combined. Transfer the cake mixture into a NON-GREASED tube pan and bake at 160 degrees for about 40-45 minutes, or until a skewer inserted withdraws clean. If the top cracks or becomes too dark, cover it with aluminum foil and continue baking.
Once baked, invert the pan and place it on a raised wire rack to cool completely. Use a small palette knife to gently scrape along the side of the pan, including the edge of the tube and the bottom, to unmold the cake. Enjoy the delicious pandan cake!