Cream the softened butter with both sugars for 3 minutes until light and fluffy.
Beat in the eggs one at a time, then mix in the vanilla extract.
Whisk together flour, cornstarch, baking soda, and salt in a separate bowl.
Fold the dry ingredients into the wet mixture until just combined.
Fold in the milk chocolate chips.
Chill the dough for at least 30 minutes, or up to 24 hours for best flavor.
Preheat oven to 350°F (175°C) and line baking sheets with parchment paper.
Scoop dough into balls and place 2 inches apart on the baking sheet.
Bake for 9-10 minutes until edges are golden but centers still look soft.
Sprinkle with flaky sea salt if desired, then cool on the tray for 5 minutes before transferring to a wire rack.
