In a large mixing bowl, whisk together the all-purpose flour, baking soda, salt, cornstarch, and premium matcha powder until well combined.

In a stand mixer, combine the room-temperature unsalted butter, white sugar, and light brown sugar. Beat until light and fluffy.

With the mixer running on low speed, add the large egg, egg yolk, and vanilla extract. Beat until smooth.

Gradually add the dry mixture into the wet ingredients, mixing on low until just combined.

Gently fold in the white chocolate chunks and red M&Ms.

Cover the cookie dough with plastic wrap and refrigerate for 30 minutes.

Preheat your oven to 350°F (180°C) and line a baking sheet with parchment paper.

Scoop tablespoon-sized portions onto the lined sheet, flatten slightly, and bake for about 10 minutes.

Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack.