Step 1: Preheat your oven to 325°F (165°C). Ensure you have a 10-inch tube pan ready, but do not grease it.
Step 2: In a large bowl, whisk together the sifted cake flour, 1 cup of sugar, baking powder, and salt.
Step 3: Create a well in the center of the dry ingredients and add the egg yolks, coconut milk, vegetable oil, and pandan paste. Whisk until the batter is smooth and free of lumps.
Step 4: In a separate, perfectly clean glass or metal bowl, beat the egg whites with the cream of tartar on medium speed until foamy.
Step 5: Gradually add the remaining 1/2 cup of sugar to the egg whites while increasing the speed to high. Beat until stiff, glossy peaks form.
Step 6: Gently fold about 1/4 of the egg whites into the pandan batter to lighten it. Then, fold in the remaining whites in two batches using a gentle over-and-under motion until no white streaks remain.
Step 7: Pour the batter into the ungreased tube pan and smooth the top with a spatula. Tap the pan on the counter once or twice to release large air bubbles.
Step 8: Bake for 50-55 minutes, or until the top of the cake is golden brown and a wooden skewer inserted into the center comes out clean.
Step 9: Immediately invert the pan onto a wire rack or a bottle neck. Let the cake cool completely in the inverted position for at least 1-2 hours before removing it from the pan.