Whisk together the flour, cornstarch, and baking powder in a bowl. Set aside.
Beat the softened butter and cream cheese with an electric mixer for 1-2 minutes until smooth.
Add the egg, milk, and vanilla extract, mixing until fully combined.
Gradually beat in powdered sugar until the mixture becomes light and fluffy.
Fold in the dry ingredients, then stir in the mini chocolate chips. Cover and chill for 1 hour.
Heat the oven to 375°F (190°C) and line two baking sheets with parchment paper.
Roll the chilled dough into 24-26 balls, placing them 1.5 inches apart on the baking sheets. Lightly flatten each one.
Sprinkle a few more mini chocolate chips on top for extra indulgence.
Bake for 10 minutes until the edges are lightly golden. The centers should look slightly underbaked for a soft texture.