Cream the butter and sugar: add sugar into softened butter, beat using an electric mixer until light and fluffy.
Add egg and vanilla extract into the creamed butter and sugar, beat until fully combined.
Mix the dry ingredients: cake flour, matcha powder, baking powder, baking soda and salt. Sift the dry ingredients into the mixture, mix together using a spatula.
Add chocolate and walnuts and mix together again.
Scoop the cookie dough onto a baking pan (lined with baking paper), around 60g each. Flatten each dough a little bit.
Preheat the fan oven to 180°C and bake for 15 minutes.