To a bowl add butter and sugar and cream until pale and fluffy using a spatula. A hand mixer can also be used.
Then, add egg yolk and milk. Mix until well combined.
Sift in cake flour, corn starch and salt.Then, add tea and mix until well combined. Transfer dough to a piping bag. Pipe dough onto baking sheet lined with parchment paper. Bake in preheated oven, rack in middle position, at 350oF (180oC) for 15-18 minutes.
Let cookies cool on the baking sheet for 5 minutes and then transfer to wire rack to cool completely.