Prepare the Dry Mix: In a medium bowl, mix together the flour, cornstarch, and baking powder. Set aside.

Cream Butter and Cheese: In a big bowl, use an electric mixer to blend the butter and cream cheese until smooth.

Combine with Sugar: Gradually add the powdered sugar to the creamed mixture, beating until light and fluffy.

Add Wet Ingredients: Mix in the egg, milk, and vanilla extract until well combined.

Combine Dry and Wet: Gently fold the dry flour mixture into the wet ingredients until just combined.

Fold in the chocolate chips, being careful not to overmix.

Cover the dough and chill in the refrigerator for at least 2 hours.

Preheat oven to 350°F (175°C) and scoop dough onto lined baking sheets.

Bake for 10-13 minutes until the edges are just set but the centers are still soft. Cool on the pan for 10 minutes before transferring to a wire rack.