• Line two large baking sheets with parchment paper. Preheat the oven to 350 F (180 C) for conventional oven, 330 F (165 C) for convection oven
• About 30 minute to 1 hour before you plan to bake, get the butter, whole egg, and egg yolk out from the fridge to and let them come to room temperature

Prepare the cookie dough:

• Combine all-purpose flour, baking soda, salt, cream of tartar in a bowl and whisk to combine
• In a bowl of a standmixer, fitted with a paddle attachement or regular mixing bowl (if using a handmixer), add softened butter and sugar. Beat the butter over medium speed (speed 6 or 8 on KA) until they are creamy, about 3 minutes.
  
• Then add whole egg, egg yolk, and vanilla and beat again until combined, another minute
  
• Add the flour mixture. Use the paddle to give everything a stir a bit before starting the machine so the flour mixture won't "fly" all over
  
• Start mixing on the lowest speed until just combined. Don't overmix it
  
• Transfer the cookie dough out from the bowl
  
• Divide the dough into two. Add half of it back into the bowl and add matcha powder and beat just until combined
  
• Add finely chopped white chocolate to the other and beat until just combined
  
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• The total weight of dough for each cookie I made is about 50 grams (about a bit less than 1/4 cup). So you can get 25 grams of matcha dough and 25 grams of white chocolate dough. Roll each into a ball and "attach" them together and smooth into a dough ball
  
• 
• You can also do two matcha doughs and two white chocolate doughs
  
• Arrange the dough pieces so that they are alternating between the two
  
• Instead of half and half look, you have an alternate color between matcha and white chocolate
  
• Coat each dough ball with sugar
  
• Place the cookie dough on a baking sheet, about 2 inches apart because they will spread
  

Baking:

• I recommend baking one tray at a time for the best result. Place the baking sheet on the middle rack and bake for 10-11 minutes, rotate halfway through baking.
  
• The cookies will puff up and the center may still appear soft. Continue baking the next batch. If you only have one pan, you need to let the pan cool down completely before baking the next batch of cookie dough
  
• Let the cookies cool on the pan for 10 minutes and then transfer to cooling rack to let them cool down completely. The cookies will flatten after cooling down and that's the way it supposed to be
  

How to store:

• Once the cookies have cooled down completely, store them in an air-tight container, in a cool dry place for about 2 days
• Find more details on how to store unbaked cookie dough and other tips in the post below