Prep: Heat your oven to 340°F (170°C), placing the rack in the lower third. Have your ungreased 17cm (7-inch) aluminum chiffon pan ready. Sift 80g of pastry flour and 3g of baking powder together twice to ensure it is incredibly light.
Yolk Batter: In a bowl, whisk the egg yolks with 15g of sugar until pale. Slowly stream in 30g of Taihaku sesame oil and whisk until fully emulsified. Whisk in the mashed banana mixture and 28g of whole milk.
Finally, sift the dry flour mixture over the top and whisk just until smooth—do not overmix.
Meringue: In a separate, impeccably clean bowl, beat 140g of egg whites until foamy. Add 45g of sugar in three separate additions. Beat until you reach firm, glossy peaks that have just a slight bend at the tip (bird's beak).
Fold: Whisk one-third of the meringue into the yolk batter to lighten it. Then, gently fold in the remaining meringue in two additions until the batter is just uniform. Pour the batter into your pan and run a wooden skewer through the batter once in a circle to release any large trapped air bubbles.
Bake (Stage 1): Bake at 340°F (170°C) for 30 minutes without opening the oven door.
Bake (Stage 2): Lower the temperature to 320°F (160°C) and bake for 10 more minutes. The cake is done when a skewer inserted into the tallest crack comes out clean, and the top springs back when gently pressed.
Invert and Cool: Remove from the oven and invert the pan immediately. Let it cool completely upside down for at least 2 hours to prevent the airy crumb from collapsing.
Unmold: Once completely cool, run a thin offset spatula around the outer wall and the center tube to release the cake. Carefully remove the base. Slice with a serrated knife using a gentle sawing motion.
Decorate (Optional): This cake is delicious on its own, but to elevate it for a special occasion, top the completely cooled cake with a generous swoop or piped design of stabilized vanilla Chantilly cream. Gently arrange the fresh banana slices and edible flowers over the cream just before serving.