Measure and sift 100 g of plain flour and set aside.
Measure 95g of plain flour and 5g of matcha powder. Sift together and set aside.
In the bowl of an electric mixer fitted with the whisk attachment, cream the butter and sugar until it becomes a white creamish colour.
Separate the egg yolk and egg white. Set aside the egg white for later use to glue the cookie doughs together.
Add the egg yolk to the electric mixer and blend the egg yolk on low speed for a minute.
Divide the creamed butter mixture into half. *3 Leave half in the electric mixer bowl. Change the attachment to a flat beater attachment and gradually add the 100g of plain flour with the mixer on low speed.
When all the flour is combined and has become crumbly, take out the dough onto a sheet of cling wrap. Wrap the dough with the cling wrap and shape the dough into 2x4x20cm long board and refrigerate for 30 minutes.
Repeat step 7 for the remaining creamed butter and matcha powder combined flour.
Take out both dough and remove the cling wrap.
Place the plain dough on a clean work surface.
Using a sharp knife, slice the dough in half.
Brush the cut surface of the palin dough with leftover egg white, then place the matcha dough on top of the plain dough.
Cut it in half again.
Place the half of the dough on the clean surface, brush the top with egg whites. Place another half on top of it in a way that the plain colour and matcha colour alternate.
Gently press together and wrap with a cling wrap sheet and rest it in the fridge for at least one hour. (I left it in the fridge overnight)
Preheat the oven to 160°C (338°F).
Line a baking tray with a baking sheet. Take out the cookie dough from the fridge.
Slice it about 5mm(0. inch) thick and place on the baking tray.
Bake them for 20 minutes
Remove baking tray from the oven and let the cookie cool on a cooling rack.
*1 separate 1 large egg weigh about 50g. Keep white egg for later use. *2 Total amount required.*Baking time is indication only. If you don't like the plain part of the dough becoming brown, move the baking tray to a lower rack in the last 5 minutes of baking.*They can be made ahead and refrigerated for a couple of days or frozen for a month.*Store the baked cookies in an airtight container for a few days.