In a medium bowl, whisk together the all-purpose flour, matcha powder, baking soda, and salt. Make sure there are no matcha lumps.

In a large bowl, using an electric mixer on medium speed, beat the room temperature unsalted butter, granulated sugar, and packed light brown sugar until light and fluffy, about 2-3 minutes. Scrape down the sides of the bowl as needed.

Add the room temperature large egg and vanilla extract to the creamed butter mixture. Beat on medium speed until just combined, about 1 minute, being careful not to overmix.

Gradually add the dry ingredient mixture to the wet mixture, mixing on low speed until just combined and no streaks of flour remain. Be careful not to overmix, as this can lead to tough cookies.

Using a rubber spatula, gently fold in the white chocolate chips or chunks until evenly distributed throughout the dough.

Cover the bowl with plastic wrap and chill the cookie dough in the refrigerator for at least 30-60 minutes. This helps the flavors meld and prevents the cookies from spreading too much.

Preheat your oven to 375°F (190°C). Line two baking sheets with parchment paper. Scoop rounded tablespoons of dough (about 1.5 tablespoons per cookie) onto the prepared baking sheets, leaving about 2 inches between each cookie.

Bake for 10-12 minutes, or until the edges are lightly golden and set, but the centers still look slightly soft. They will continue to set as they cool. Let the cookies cool on the baking sheets for 5 minutes before transferring them to a wire rack to cool completely.