Sift the cake flour and baking powder together.
Make the pandan juice. Cut the pandan leaves roughly. Add 25ml of water, and blend until very fine. Strain the fibres, squeezing the pulp to get as much juice as possible. It should amount to 100ml of pandan juice. If there is not enough, add more water.
Break the eggs and separate the whites from the yolks. Be careful not to break any yolks during this process. Set the egg whites aside.
Add 1/4 of sugar, all the salt, vegetable oil, pandan juice and vanilla essence to the yolks. Whisk until fluffy and well-combined.
Dump in all the flour and mix gently until just combined.
Add egg whites and 1/4 of sugar into the stand mixer with a balloon whisk attached. Start the whisk on low speed, slowly moving it to high. When the foam is getting thicker, add another 1/4 of the sugar.
When the foam is opaque white and starting to become glossy, add the rest of the sugar. Let it continue whisking for another 3-4 minutes.
Optional: gradually stop the machine and add the food colouring. Let it whisk for about 30 seconds to evenly distribute the colour. Switch off the machine and set aside.
Pre-heat the oven to 150°C/ 302°F.
Add 1/3 of the whipped egg whites to the yolk mixture. With a whisk, carefully and gently mix the batter while aerating it. Once combined, add the rest of the egg whites and slowly mix until smooth. Smoothen any lumps present in the batter.
Slowly pour out the mixture onto a clean chiffon cake tin without parchment papers laid or grease on the sides. Carefully turn the tin to level the batter out.
Place the tin in the centre rack of the oven and bake for 20 - 25 minutes. Poke the centre of the cake to check for doneness. If it comes out dry, the cake is done.
Remove the cake from the oven and place it upside down on a cooling rack. Let it cool completely for about 2 - 4 hours.
Once cooled, run a small, thin knife along the edges of the cake tin. Optionally, cut the top part of the cake to level it. Detach the cake from the sides, and run the knife along the bottom as well.
Flip it onto a serving plate and cut into the desired serving sizes. Serve as-is, with fresh berries, whipped cream, or ice-cream.