Preheat the oven to 350F (180C) degrees.
Line baking sheets with parchment paper or silicone baking mats.
Whisk together the flour, cornstarch, baking powder, baking soda and salt.
Cut the cold butter into small pieces and place in a large mixing bowl.
Mix the butter, brown sugar and white sugar until combined.
Mix in the egg and vanilla extract.
With the mixer on low speed, mix the flour mixture into the butter mixture about ½ at a time.
Turn off the mixer and stir in 1 ½ cups chocolate chips.
If the dough feels room temperature or warm to the touch, cover the bowl and place in the fridge for 30 minutes to firm up.
Form the dough into balls with about ⅓ cup of dough each. I got 8 very large cookies in total. Each weighed about 100 grams or 3.6 ounces.
Place dough balls about 3 inches apart on the lined cookie sheets. Bake 1 sheet at a time in the preheated oven for 12-14 minutes, or until the tops look just set and golden brown. Place the 2nd cookie sheet in the fridge as the first sheet is baking.
After you remove the cookies from the oven, optionally place a few extra chocolate chips on the top of each cookie. Cool on the cookie sheet for at least 15 minutes, then transfer to a wire rack