In bowl, combine the dry ingredients (flour, baking soda, salt and cornstarch) and set aside.
Using a hand mixer or a stand mixer with a paddle attachment, cream together the room temperature butter and sugars (brown and white) on medium speed (4) for about 2-3 minutes until the mixture is fluffier. Scrape down the sides of the bowl with a rubber spatula.
Add the egg and vanilla on low speed (1) and then increase the speed to medium (4) for about 30 seconds until it is incorporated.
Slowly add the dry ingredients to the wet ingredient and beat on low until it is mixed together.
Add the chocolate chips and mix on low. Stop mixing when the chocolate chips are incorporated.
Cover the bowl with plastic wrap and chill in the fridge for at least 30-40 minutes. Chilling is critical for these cookies to not spread.
While chilling, preheat the oven to 350°F (177°C) and line two baking sheets with parchment paper.
Using an ice cream scooper, (about 2 tablespoons) scoop the cookie dough into balls and place on the parchment lined pans. Make sure that the cookie dough balls are about 2 inches a part.
Bake at 350°F (177°C) for 11-12 minutes until slightly golden brown around the edges. The cookies will not look done in the center when you pull them out of the oven. They will continue cooking on the baking pan. Allow them to cool on the baking pan for 5 minutes and then transfer them to a cooling rack.
Note: If you want smaller cookies, use a cookie scooper or use 1 tablespoon of cookie dough to form balls. The bake time will be 9-11 minutes for the smaller size cookies.