This is the first time I've baked with matcha powder or green tea. (I made these cookies before I made the green tea chocolate bundt cake).  I followed the recipe exactly and I think it has too much tea in it. The tea flavour was very strong and the result was a slightly bitter tasting cookie.  I would probably add a little more sugar and less tea next time.  It was still very nice especially if eaten slowly.  I love the colour of the green tea but they turned a little brown when cooked.  
200g butter
50g icing sugar (add a little more if you prefer your cookies on the sweeter side) 
135g plain flour 
15g green tea powder (I would try using 5-10g instead but if you like strong tea flavour then stick to 15g)
50g cornflour
1/2 teaspoon vanilla extract
- Preheat oven to 180C.
 - Beat butter and sugar until creamy.
 - Add vanilla extract.
 - Sift in flour, cornflour, green tea powder and mix well until a dough is formed.
 - Scoop dough into a piping bag and pipe evenly on to a baking tray.
 - Alternatively drop tablespoonful of dough on to a baking tray.
 - Bake in the preheated oven for approximately 13-15 minutes until lightly browned.