Brew a strong chai tea concentrate and let it cool completely.
In a medium bowl, whisk together the flour, cornstarch, baking soda, salt, cinnamon, cardamom, ginger, cloves, and nutmeg.
In a large mixing bowl, beat the butter, brown sugar, and granulated sugar for 2 to 3 minutes until light and fluffy.
Add the egg, egg yolk, vanilla extract, chai concentrate, milk, and optional chai tea leaves. Mix until smooth and creamy.
Add the dry ingredients and mix just until combined. Do not overmix.
Cover the dough and chill for 30 minutes.
Preheat the oven to 350°F. Line baking sheets with parchment paper.
Combine the optional cinnamon sugar coating ingredients in a small bowl.
Scoop the dough into large 2-tablespoon portions. Roll lightly in cinnamon sugar if desired.
Arrange the cookies 2 inches apart on the prepared baking sheets.
Bake for 9 to 10 minutes until the edges are lightly golden and the centers still look slightly soft.
Let the cookies cool on the baking sheet for 5 minutes before transferring to a wire rack.
For the glaze, whisk together the powdered sugar, chai concentrate, milk, cinnamon, cardamom, and vanilla until smooth.
Drizzle the glaze lightly over the cooled cookies.