Whisk the all-purpose flour, cornstarch, baking soda, and fine salt in a medium bowl until evenly combined.
Beat the softened butter, brown sugar, and granulated sugar for 2 to 3 minutes, until creamy and slightly fluffy. Mix in the whole milk and vanilla extract.
Add the dry ingredients to the butter mixture and mix just until a soft dough forms. Fold in the semisweet chocolate chips without overmixing.
Portion the dough into 12 large mounds and place them on a lined baking sheet. Refrigerate for 45 minutes to prevent excessive spreading and deepen the flavor.
Preheat the oven to 350 degrees F. Arrange the chilled dough mounds 3 inches apart on lined baking sheets and gently flatten only the very tops.
Bake for 12 to 15 minutes, until the edges are golden but the centers still look slightly soft. Cool on the baking sheets for 10 minutes before transferring the cookies to a cooling rack.
