In a large mixing bowl, whisk together the dry ingredients (flour, soda, salt and cornstarch). Set aside.
Line a baking sheet with parchment paper or silicone baking mat. Set aside.
In a large mixing bowl, cream butter with both sugars on low speed for two minutes. Beat until light and fluffy. Scrape down the sides of the bowl as needed.
Add vanilla and egg and mix until just combined. Scrape down the sides of the bowl.
With mixer on low speed, mix in flour until just incorporated.
Stir in chocolate chips.
Scoop the dough into 1,5 tablespoon mounds of dough. Chill the balls in the fridge for at least 30 minutes or overnight.
When ready to bake, preheat the oven to 350 degrees F.
Bake cookies for 8 to 12 minutes or until the edges are set (they should have small tiny holes around it). Let sit on the baking sheet for 3 minutes to finish baking.