In a stand mixer fitted with the paddle attachment, cream the butter, granulated sugar, and brown sugar for 2–3 minutes until light and fluffy.
Add the egg, egg yolk, milk, and vanilla extract.
Mix until smooth.
In a separate bowl, whisk together flour, baking powder, cinnamon, cornstarch, salt, and baking soda.
Gradually add the dry ingredients to the wet mixture and mix until just combined.
Shape the Cookies
Scoop dough into 2-tablespoon portions.
Roll into balls and place on a parchment-lined tray.
Use the back of a tablespoon dipped in flour to create an indentation in the center of each cookie.
Fill each indentation with 2–3 teaspoons of streusel topping.