Toast black sesame in dry pan over medium heat for 3-4 minutes until fragrant. Set aside to cool completely. Add about 4 tbsps of cake flour to cooled black sesame, mix well. Process until very fine using a grinder. Sift together black sesame powder, the remaining cake flour and baking powder, mix well.
Add in a tray of water (about 2 cups) in the oven, preheat oven to 160°C/320°F.
In a clean mixing bowl, whisk egg whites on low speed until foamy. Add in cream of tartar, whisk until small bubbles are formed. Add in fine sugar gradually, whisk on low speed until stiff peak (the peaks will point straight up and hold). (Reminder: Egg whites and equipment used to beat egg whites must be grease-free and water-free, including egg yolk. It is advisable to clean the egg shells and equipment with dishwasher detergent, then dry with a clean cloth. Use a clean small bowl to separate the egg yolk and egg white, if the egg yolk cracks, don’t use that egg white.)
Combine egg yolks, salt, sugar, milk and oil, mix well. Add in flour mixture, mix until just combined.
Add meringue into batter in 4 batches, mix gently using balloon whisk.
Fold gently until well mixed with a spatula.
Tap mixing bowl on countertop for a few times to burst large bubbles, then pour batter into 22-cm loose base tube pan (do not grease), tap tube pan gently again on countertop for a few times.
Put into preheated oven, bake at 160°C/320°F for 45 minutes, then at 180°C/355°F for another 10-15 minutes, until the top is golden brown. (Reminder: The heat for different oven is different, the suggested time is only for reference, adjust the baking time base on your oven if necessary.)
Turn the pan upside down onto a wire rack (at least 6″ from the countertop), and set aside until fully cooled.
Unmold the black sesame chiffon cake when it has fully cooled down.