Adjust your baking rack to the lower third/lower middle position and preheat oven to 325F. Line a 16-cup tube pan with parchment paper (see post) and set aside.
In a large bowl, whisk 1 ½ cups cake flour, 1 ½ cups sugar, 2 tsp baking powder and ½ tsp salt until combined.
Add 2 whole eggs, 5 egg yolks, ¾ cup water, ½ cup oil and 2 tbsp ube extract and whisk until smooth.
Using an electric hand mixer or a stand mixer fitted with the whisk attachment, whip 5 eggs whites with ½ tsp cream of tartar on medium speed until foamy. Switch to medium-high speed and whip until stiff peaks form.
Add egg whites to your egg yolk mixture and fold until incorporated and you don't see streaks of egg whites remain. Handle carefully so as not to deflate the air out of your egg whites.
Transfer your cake batter into your tube pan and smoothen the top with a spatula. Gently tap the pan on your counter a few times to release any air bubbles. Bake for 30 minutes, rotate the pan, then bake for another 30 minutes or until a bamboo skewer inserted into the cake comes out with minimal dry crumbs.
If your tube pan has “feet” on its rim, invert pan to cool cake. If your pan doesn’t have feet, invert your pan over the neck of a bottle so that the air can circulate. Cool completely; about a couple of hours.
To remove, run a thin knife around the edges of the pan to loosen the cake then gently tap upside down (I like catching the cake onto a piece of parchment paper or on a cutting board). Peel off parchment paper on the bottom of the cake, turn the cake right side up on a cake platter and enjoy!
See post for chiffon cake troubleshooting guide, how to line a tube pan and the complete step-by-step photos.
Ube chiffon cake can be stored on the counter at room temperature for up to 2 days and in the fridge for up to 4 days.