Cream butter, baking powder, baking soda, salt, and sugar.
Add egg and yolk and mix until homogenous
Add flour and mix to combine into dough.
Split dough in half. Mix matcha into one half until the dough is evenly green.
Pat each color dough into a rectangular box about 2x2x6 inches. Wrap each in plastic wrap and chill at least 20 minutes or until firm.
After chilling, unwrap your dough and slice each rectangular log into thirds. Then rotate 90 degrees and slice into even thirds again, creating 9 equal strips of each dough.
Place one strip of white dough in between two strips of green dough. Then layer one strip of green dough in between two strips of white dough on top. Then finish the box by adding the third layer of one strip of white dough in between two strips of green. This is your checkerboard pattern. Repeat with the remaining strips to form the second rectangular box of dough.
Rewrap the rectangles of dough in plastic and put it in the fridge to chill again, at least 20 minutes but up to overnight.
When ready to bake, preheat oven to 350 degrees and line three baking sheets.
Slice the rectangles of dough to form 2x2 inch squares about 1/4 inch thick. Sprinkle with sanding sugar, if using.
Place cookies on baking sheets and bake for 8-10 minutes.
The baking powder and baking soda add a little air and flavor to the cookie dough, but if you really want to maintain sharp edges, omit these leaveners to prevent any unnecessary spreading.