Sift cornstarch, cake flour, and green tea powder together. Set aside.

Beat soft butter in a mixing bowl. Add powdered sugar and sugar and mix.

Add yolks and milk and mix well. Add flour mixture and mix (don't over mix).

Let the dough rest for 30-60 minutes in the refrigerator.

Roll out dough to 1/4" thick and cut out with cookie cutter.

Bake at 350F (175C) in preheated oven for 10-13 minutes.

Cool completely on cookie rack, and decorate with chocolate if you want.