Whisk flour, matcha powder, baking soda, and salt together until evenly blended, ensuring no clumps remain for a smooth dough base.
Beat butter with both sugars until fluffy and pale, creating air pockets that keep cookies soft and chewy after baking.
Mix in egg and vanilla extract until fully incorporated, ensuring a smooth and cohesive wet mixture.
Combine dry ingredients with wet mixture gradually, folding gently to avoid overworking the dough.
Fold in white chocolate chips and chill dough briefly to improve structure and flavor depth.
Shape into balls and bake at 175°C for 10–12 minutes until edges are set but centers remain soft.