Place chopped pandan leaves into a blender or food processor and add water. Process to a pulp. Note: Depending on your blender, you may need to add 1 - 2 tbsp more of water to get the blades turning well enough to process.
Place the pulp in a metal strainer. Press the back of a spoon against it to obtain the juice. Set aside 1 tbsp. The leftover can be kept chilled.
Make the batter:
Preheat oven to 170°C (338°F). Position the oven rack on the lowest in the oven.
Have a 20-cm (8-inch) chiffon tube pan ready. DO NOT GREASE.
Sift together the cake flour, baking powder and salt.
In a separate, large mixing bowl, whisk egg yolks and sugar until thick and fluffy, about 3 to 5 minutes. Stir in the coconut milk, oil, pandan juice and pandan paste. Stir with a whisk until until well combined.
Add the sifted flour mixture in 2 additions. Stir with a whisk until all the flour is incorporated and no streaks of flour are visible. The mixture should be thick, smooth and free of lumps.
Make the meringue:
Fit an electric mixer with a whisk attachment. In a dry, grease-free mixer bowl, pour in egg whites and sprinkle cream of tartar over.
Whisk on medium speed (speed 4 on my Kitchen Aid). When the egg whites become frothy, add sugar bit by bit in a steady stream. Whip until stiff peaks form. This may take 5 to 7 minutes, depending on your mixer and speed.
Fold the meringue into the batter:
Add ⅓ of meringue (whipped egg whites with sugar) to the batter. Fold in gently with a whisk until well incorporated.
Add another ⅓ of the meringue and again, fold in gently.
Add the remaining meringue and fold in gently. The final batter should feel light, and have no visible streaks of meringue.
Pour into the chiffon tube pan from one place, and let the batter spread to fill the pan.
Gently run a thin spatula in an 'S' motion throughout the batter to reduce large air pockets. Smooth and level the surface. Give the pan a few taps on the counter top to minimise air pockets.
Baking and cooling:
Bake on the lowest rack in the oven for 45 to 50 minutes, or until done. DO NOT open the oven door. Only do so about 5 minutes before the end of baking, to test if done. The cake is done when a skewer inserted into the centre comes out clean. Note: A bit of cracking on the surface of the cake as it bakes is perfectly alright!
Immediately invert the pan over a bottle neck once it is removed from the oven. Allow it to 'hang' until completely cooled.
To release the cake, run an offset spatula gently around the sides of the pan, pressing against the pan as much as possible.
Then invert the pan again so that the bottom is now facing up. Gently tap or push the pan's base to loosen the cake from the sides of the pan. Then run the spatula around the base to release the funnel.
Chiffon cake is served 'upside-down'.
Storing pandan juice: The unused pandan juice can be stored in an airtight container and chilled in a refrigerator. It will keep well for up to 5 days. If pandan juice is unavailable, you may use 3/8 tsp of pandan paste in place of 1/4 tsp pandan paste.
1. Use the right pan
Chiffon cakes are best baked in a chiffon tube pan without non-stick coating. DO NOT GREASE THE PAN.
2. Use the appropriate pan size
In order for the cake to rise straight and tall, use the appropriate sized pan. When the pan is filled with batter, it should not be more than 3/4 full.
3. Have ingredients at room temperature, including eggs
Cold egg whites do not whip up as well, so it won’t trap as much air as egg whites at room temperature. When blooming cocoa, remember to allow it cool to room temperature before incorporating it into the rest of the batter.
4. Whip meringue to the ideal stiffness
5. Sift powdered ingredients together
This will give you a smoother and finer cake crumb and enable the cake to rise evenly and uniformly.
6. Do all your mixing, stirring and folding with a whisk
The meringue will incorporate more easily and thoroughly, with minimal loss of volume due to the inherent shape and structure of the whisk. It also helps reduce or eliminate air pockets in the batter.
7. Invert the chiffon pan once out of the oven
Once removed from the oven, immediately invert the pan over a bottle neck once it is removed from the oven. Or if you have tube pan with ‘feet’, invert the pan over a cooling rack. Allow it to ‘hang’ in this position until completely cooled.