Mix almond powder, powdered sugar and green tea, sieve twice and cool in refrigerator.
Heat oven to 210°C.
Cover oven tray with baking paper.
Place egg white into a bowl. Divide granulated sugar into three and add to the egg white 3 separate times to make firm meringue (not too soft).
Add almond powder/sugar/green tea mix to meringue in two stages, mixing with a flat spatula.
When well mixed, smooth the dough by pressing it to the bowl surface and turning it over repeatedly, approx. 10 times.
Put the dough into a pastry bag with nozzle and squeeze the dough onto the oven tray, they should be about 2.5 cm diameter. Keep the tray at room temperature and when the surface gets dry (about 30 minutes), put it into the oven at 210°C for 2 minutes. Reduce temperature to 150°C and bake for a further 13 minutes.
Remove tray from oven and cool macarons until they can be handled. Gently remove from tray.
Soften the butter.
Mix green tea powder gradually into the warm water and place in a saucepan.
Add milk, mix, then heat until simmering.
Put egg yolk into a bowl and add granulated sugar.
Mix well until it is white.
Add milk with green tea to egg yolk/sugar mix. When combined, pass through a fine sieve and return to the pan.
Return milk mixture to heat, stir until it gets creamy, then remove from heat.
Place into a bowl and beat until thick, even after the temperature cools.
Add softened butter gradually, mixing until it reaches a smooth consistency.
Put the finished cream into a bag with nozzle and squeeze onto bottom puff. Place second puff on top.
Put finished macarons in the refrigerator to rest.