Preheat the oven to 350˚F. Grease a 9"×13" pan and set aside.
Add the flour, baking soda, salt, and cornstarch to medium mixing bowl and whisk until combined.
Add the butter, sugars, milk, and vanilla to a large mixing bowl. Beat until combined.
Add the dry mixture to the wet and mix until combined.
Fold in 1 cup chocolate chips.
Press the cookie dough evenly into the prepared pan. Top with the remaining 1/4 cup chocolate chips and gently press in.
Bake in the preheated oven for 16-18 minutes, until a toothpick comes out clean or with just crumbs.
Allow to cool slightly and slice into 24 bars.