In a large mixing bowl, beat the softened unsalted butter with light brown sugar and granulated sugar until the mixture is light, fluffy, and pale in color, about 2 to 3 minutes on medium speed.
Crack in the large egg and pour in the vanilla extract. Beat again until fully combined.
In a separate bowl, whisk together the all-purpose flour, cornstarch, baking soda, and salt.
Gradually add the dry ingredients to the wet mixture, beating on low speed or folding with a spatula just until incorporated.
Fold in 1 cup of semi-sweet chocolate chips, making sure they’re evenly distributed. Save a few extra chips to sprinkle on top before baking.
Preheat oven to 350°F (175°C). Drop rounded tablespoons of dough onto a lined baking sheet, spacing 2 inches apart. Press extra chips on top. Bake for 9 to 11 minutes until edges are set but centers still look soft.
Allow cookies to cool on the baking sheet for 5 minutes before transferring to a cooling rack. Enjoy warm or store for later.