In a medium bowl whisk together the flour, cornstarch, baking soda, and salt. Set aside.
In the bowl of a stand mixer combine the sugar, brown sugar, oil, and vanilla extract. Using the paddle attachment beat on medium speed for 1 - 2 minutes. Scrape down the bowl as needed. The mixture will look like wet sand.
Add in the flour mixture and beat on low for 1 minute. With the mixer running, add the first 2 tbsp of milk. Continuing adding more milk until the dough comes together.
Add in the chocolate chips and mix just until combined. The dough will be sticky.
Place the dough in a bowl and cover with plastic wrap. Refrigerate the dough for 2 - 24 hours.
Preheat the oven to 350 degrees and line a baking sheet with parchment paper.
Spoon balls of dough (about 1 1/2 tbsp each) onto the baking sheet. Space the balls a few inches apart (I usually do 12 per half sheet). Bake for 11 - 13 minutes, just until the edges are golden brown. Remove from the oven, cool on the baking sheet for 5 minutes and then transfer the cookies to a cooling rack to finish cooling.