In a large mixing bowl with electric mixer fitted with paddle attachment, beat butter and sugar until creamy. Add egg and vanilla extract, mix until well combined.

In a separate bowl, prepare dry ingredients. Combine flour, baking powder, matcha powder, earl grey tea leaves (removed from tea bags), and salt together.

Add dry ingredients into the butter-egg mixture, until well combined.

Divide the dough into half. Wrap each dough with plastic wrap and chill in the fridge for at least 2 hours or overnight.

Preheat the oven to 350°F. Line two baking sheets with parchment paper or grease with cooking spray.

Take a disc of chill dough from the refrigerator. Dust the kitchen counter and rolling pin with flour. Roll out the disc to about 1/8 inch (for thinner cookies), or 1/4 inch (for thicker cookies). Continue to flour the working surface as needed. Repeat with the second disc of chilled dough. 

Bake for 9-10 minutes, or until edges become golden brown. Allow cookies to cool completely before decorating.