Line 2 rimmed baking sheets with silicone baking mats or parchment paper; set aside.
In a medium sized bowl, Whisk together flour, matcha powder, salt, and sesame seeds (if using); set aside.
Place butter and both sugars into the large bowl of an electric stand or hand mixer; cream on high speed for 3-4 minutes, or until mixture is very light and fluffy, scraping down sides of bowl as necessary. (Because there's no leavening agent in this recipe, you want to incorporate lots of air into the dough)
Reduce mixer speed to medium and add egg and vanilla extract, mixing until fully incorporated. Reduce speed to low and add flour mixture, mixing just until combined (you may still have some flour showing). Turn off mixer and incorporate white chocolate by hand with a wooden spoon or spatula.
Use a small cookie scoop or your hands to form 18 balls of dough. Space evenly on prepared baking sheets, about 1/4 inch apart. Use your fingers to gently press down on each ball of dough to flatten slightly. If desired, sprinkle tops of cookies with a few more sesame seeds.
Bake in preheated oven for 9-10 minutes, or until bottom of cookies are barely golden and tops are still somewhat shiny. Don't over bake, as cookies will continue to bake after being removed from the oven.
Allow cookies to cool on pan for 2 minutes before transferring to wire racks to cool completely.
This recipe for Matcha White Chocolate Cookies was created by ItsYummi.com. https://www.itsyummi.com/recipe-for-matcha-white-chocolate-cookies/ is copyrighted and may not be used without prior consent in writing from the owner.