Divide the yolks and whites. Chill the egg whites until you need them.
Sift the cake flour, baking powder and cornstarch together.
Cut the kabocha squash into bite sized pieces, and steam in a steamer or microwave until tender.
Mash the kabocha squash while still hot.
Put the egg whites in a bowl and mix until it turns watery. Add half the sugar and whip with a hand mixer to make the meringue.
When the meringue is thick and forms soft peaks, add the rest of the sugar and beat.
When it forms stiff peaks as in the photo, it's ok. Chill in the refrigerator.
Put the egg yolks in another bowl, add the sugar and mix.
Beat until the yolks turn pale and forms a thick ribbon.
Add the vegetable oil and milk, then mix well.
Add the mashed kabocha squash from Step 4.
Sift the flours again, right into the bowl.
Blend with the hand mixer until the batter is no longer floury.
Add 1/3 of the meringue from Step 7 to the batter, and mix with the hand blender.
When it is blended, add 1/2 of the remaining meringue. Use a rubber spatula this time, and a cut-and-fold motion to mix.
Lastly add the batter to the bowl containing the meringue. Mix gently to maintain the airy texture of the meringue.
When it's evenly mixed, pour the batter into the cake pan. Drop the filled cake pan 2 to 3 times onto the counter top to eliminate air bubbles.
Bake in a preheated 340°F/170°C oven for 40 minutes. If it looks like the surface is becoming burned, cover it with foil.
Cool upside down on a bottle or mug and it's done.
Story Behind this Recipe
I wanted to make a Halloween-like kabocha squash sweet.
Be sure to make a firm meringue. If you steam the kabocha squash, the nutrition in it will become nice and concentrated. The cake is very moist, and doesn't taste strongly of kabocha squash, so I recommend it for children who don't like kabocha squash too.