In bowl, combine flour, cornstarch, baking powder, and salt - mix.

Add egg, sugar, butter, lemon zest, and vanilla - mix well until a doughy texture is formed.

Remove and place on floured surface.

Flatten a bit, and add ground pistachios to middle of dough.

Begin kneading until pistachios are well mixed and it becomes a soft dough.

Break off piece and roll into small ball (about 2 inches) and place on baking sheet lined with parchment paper (or greased with butter), and flatten slightly.

Repeat until all dough is used.

Place in preheated oven at 400F for 10-12 minutes, or until golden brown.

Remove and let cool.

Serve!

- Makes about 12 cookies