Preliminaries: Line the mold with kitchen parchment paper. Leave the eggs in the refrigerator until you need them. Sift the cake flour and matcha together 3 times.

Put the egg whites in a bowl, and whip with a handheld mixer. (Make sure that you use an impeccably clean bowl. If it has any water or oil in it the egg whites won't whip up properly!)

When the egg whites are evenly whipped, add 1/2 of the granulated sugar and whip together. When it's very fluffy add the rest of the sugar, and keep whipping until it turns into a smooth, glossy meringue.

If stiff peaks form when you lift up the mixer, it's done! (You must make a meringue that forms stiff peaks!)

Add the yolks to the meringue and mix well.

Add the sifted flour and matcha all at once.

Fold the flour into the meringue in a cut-and-fold motion, mixing up from the bottom. (Do not beat the batter and mix as little as possible)

Put the butter and milk into a heatproof bowl, cover with plastic wrap and microwave for 60 to 80 seconds or so.

Mix to dissolve the butter. (Keep mixing until it cools down to about 50 °C.)

Add the butter-milk mix to the batter a little at a time. (If you add it all at once it will sink down to the bottom! Add it in 3 to 4 batches.)

Mix it in using a cut-and-fold motion, working rapidly. (Do not beat the batter and mix as little as possible!)

Pour the batter into the lined mold. (Since the batter at the bottom of the bowl does not rise well, pour it around the perimeter of the mold, where it will cook faster.)

Drop the mold from a height down on your work surface 2 to 3 times to eliminate any air pockets, and smooth out the surface.

Bake for 30 to 40 minutes in a preheated 170 °C oven. If you poke the middle with a bamboo skewer and it comes out clean, it's done! As soon as it's baked, drop it from a height of 20-30 cm onto your work surface to prevent the cake from shrinking.

Put a well wrung out moistened kitchen towel on your work surface, and take the spongecake out of the mold. Peel the paper off the sides. (Put the cake top side down.)

Put the mold back on the cake and leave for 2 to 3 minutes. (This is to make the top surface flat, and to even out the moisture in the cake.)

Take the mold off and peel off the paper from the bottom.

Turn the cake over, and cool on a cake rack.

Cover the spongecake with a moistened and tightly wrung out kitchen towel, and leave to cool.

When the spongecake is cool, slice horizontally and fill with the fillings of your choice, such as whipped cream. (The cake is easier to slice if you let it rest for a day. Keep in a plastic bag). I recommend spreading the cake with cream, then letting it rest for a day! It will become even more moist.

How to slice the spongecake cleanly: Mark the sides vertically with a knife so that you can re-stack the layers later.

If you don't have a cake slicer: Insert toothpicks where you want to slice through the cake, starting with the upper layer, spacing the toothpicks evenly (in 4 to 8 places).

Slice through the cake on top of the toochpicks horizontally. Slice the lower layer in the same way.

Re-stack the layers, following the vertical marks you made in Step 21.