Step 1: In a large bowl or stand mixer, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy (about 3-5 minutes).
Step 2: Add the eggs one at a time, beating well after each addition, then stir in the vanilla extract.
Step 3: In a separate bowl, whisk together the flour, baking soda, salt, and cornstarch.
Step 4: Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Do not overmix.
Step 5: Fold in the chocolate chips by hand using a spatula.
Step 6: Cover the dough and refrigerate for at least 2 hours or overnight.
Step 7: Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
Step 8: Scoop rounded tablespoons of dough onto the baking sheet, spacing them 2 inches apart.
Step 9: Bake for 9-11 minutes, or until the edges are lightly golden but the centers still look slightly soft.
Step 10: Let the cookies cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.