Shift the flour, soya powder and baking powder. Preheat the oven to 340°F/170°C.
Separate the egg yolks and whites. Put the egg whites in the fridge until you need it. Mix in the sugar with the egg yolks and whisk well.
Once the mixture is pale, add vegetable oil and whisk well. Add milk and the dry ingredients and whisk well.
Dissolve the ■ matcha in hot water and mix in the kuromitsu.
Add a pinch of salt to the egg whites and mix with cutting motion first. Divide the granulated sugar into 3 portions. Add a portion at a time and whisk well after each addition.
Whisk until the bubbles are rough-textured. Change the whisk to an electric mixer and whisk at highest speed until you have a smooth and shiny meringue.
When you lift the meringue and its peak gently falls, reduce the speed of the mixer and whisk until really smooth.
Scoop a small amount of the meringue from Step 7 to the egg yolk mixture from Step 3 and stir with a whisk.
Scoop another small portion of the meringue to the egg yolk mixture and fold in with a spatula. When you add the meringue, stir well with a whisk without crushing the delicate bubbles.
Pour the egg yolk mixture into the rest of the meringue and fold in with a S shape motion. Stir well until all lumps are gone.
Put three ladles of the batter from Step 10 into another bowl and add the matcha and kuromitsu mixture from Step 4. Stir quickly.
Stir the Step 10 batter again with a spatula. Pour the Step 10 batter into a mould and add a small portion of the Step 11 batter. Stir lightly.
Add the rest of the Step 10 and 11 batter and stir lightly and evenly, lifting from the bottom of the mould with a spoon.
In the end, stir with a stick along the mould to stick the batter to the edge of the mould. Bake in a 340°F/170°C oven for 20 minutes and reduce the temperature to 320°F/160°C. Bake for another 15 to 20 minutes.
Bake until a skewer inserted into the middle comes out clean. Take out from the oven and leave to cool upside-down on a bottle big enough to support the mold.
Story Behind this Recipe
I thought green tea would make a beautiful marble pattern and I made Japanese-style chiffon cake. I modified a usual basic chiffon cake recipe.
Baking powder is not always necessary, but when it's easy to push the meringue batter down while you're marbling it, so it's there just in case.