Melt butter: add butter to a small fry pan over low heat and gently melt. Once melted, turn off the heat and let the butter get to room temperature, about 15 minutes.
Cream butter with sugar: add sugar to a mixing bowl and pour over melted butter. Using a standard whisk, whisk until light and creamy, about 1-2 mins. Add egg and vanilla and whisk again until combined, 1-2 minutes.
Add dry ingredients: add in flour (sifted), matcha (sifted), baking powder, baking soda and salt. Mix until combined using a spatula then fold in the chopped oreos.
Roll into balls: roll into golf sized balls, makes about 16 cookies. Add to a baking paper lined plate and place into the fridge for 30 minutes. Meanwhile, preheat oven to 175C/350F.
Bake: Add to a baking paper lined tray, evenly spread apart by 2 inches and bake for 8-9 minutes (8 minutes for a more gooey center).
Cool: let cookies cool on the tray for 1-2 minutes, then transfer the cookies on the baking paper onto a cooling rack or cool surface and let cool for 10 minutes.
