Preheat oven to 350°F. Line two baking sheets with parchment paper.
Whisk flour, cornstarch, baking soda, and salt in a medium bowl; set aside.
Beat softened butter, cream cheese, granulated sugar, and brown sugar until light and fluffy, 2–3 minutes.
Mix in vanilla and milk until smooth.
Add dry ingredients in two additions; mix on low just until the dough comes together.
Fold in mini chocolate chips until evenly distributed.
Chill the dough for 15 minutes to firm slightly for easy scooping.
Scoop about 1½ tablespoons of dough per cookie and arrange 2 inches apart on prepared sheets.
Bake 10–12 minutes, until edges look set and centers are still pale and soft.
Cool on the sheet for 5 minutes, then transfer to a rack to finish cooling.