First add the butter, ½ cup of the sugar, and the matcha powder to a mixing bowl and cream together until light and fluffy, about 1 minute. Then, add in the flax egg and vanilla extract and whip together about 10 more seconds to combine.
Next, add in sifted flour, baking powder, and salt to the mixing bowl. Mix until a thick, yet slightly sticky, cookie batter forms. Do not overmix or else you will form too much gluten and the cookies will not spread as much and will be tough.
Next, cover the mixing bowl of dough and add to the fridge to chill for 30 minutes- 1 hour.
Cover a baking sheet in parchment paper and preheat the oven to 350F. Next, remove the dough from the fridge and use a 2 Tbsp cookie scoop to form your cookie dough (about 45 grams of dough per cookie). Roll into balls between your palms and then roll in the 2 Tbsp of sugar that was set aside so that each dough ball is coated in sugar.
Place the matcha cookie dough balls onto the baking sheet. Then, slightly press each dough ball down with your palm. Make sure that each cookie is kept about 2 inches apart since they will spread slightly while baking.
Bake for 11-13 minutes until bottoms are lightly browned and the cookie is cooked, but still has soft centers. The cookies will continue baking after they are removed from the oven so the centers should be soft and just cooked, but not glossy or raw, when they are removed from the oven. Please be careful not to overcook these cookies as they will still be soft but will lose their "chewy" texture if overcooked.
Remove the cookie tray from the oven and immediately tap the tray on the counter to produce a more “wrinkly” cookie. Then, let the cookies cool on the baking sheet for 5 minutes. The cookies will be soft and puffy out of the oven and will naturally deflate a little while cooling.
Once the cookies have cooled, serve and enjoy!