Grease and line 9-inch (23-cm) round baking pan with parchment paper.
*Pandan juice: Blend together 60 ml of water and 15 g of pandan leaves until fine, extract 60 ml of pandan juice.
Preheat oven to 160°C/320°F (you may add in a tray of water, about 2 cups, to increase the humidity, which helps cake bake evenly).
In a clean mixing bowl, whisk egg whites over low speed until large bubbles are formed. Add in cream of tartar, whisk until small bubbles are formed. Add in sugar gradually, whisk until stiff peak (the peaks will point straight up and hold).
Beat egg yolks and sugar until thick, add in corn oil, beat until combined, add in pandan juice, mix well. Sift together cake flour and baking powder, then sift again into egg yolk mixture, mix until just combined.
Add meringue to batter in 3 batches, mix gently using a balloon whisk. Fold gently until well mixed using spatula, then tap mixing bowl on countertop for a few times to burst large bubbles. (Reminder: Do it quick but gentle to avoid deflating the meringue. Scrape the bottom of mixing bowl with spatula and fold over, repeat folding motion until just well mixed.)
Pour batter into baking pan, tap baking pan again for a few times.
Bake at 160°C/320°F for 25 minutes, then increase to 180°C/355°F and bake for another 10-15 minutes, or until fully cooked (wooden stick inserted in the center of the cake comes out clean).
Once remove from the oven, drop the baking pan from 1 foot high onto the countertop (to minimize shrinkage).
Unmould the pandan sponge cake and set aside on wire rack until completely cooled.