Cube the cold unsalted butter and place it in a mixing bowl. Cream the butter with brown and granulated sugars using an electric mixer on medium speed for about 4-5 minutes, until light and fluffy.

Add the cold eggs one at a time, mixing well after each addition until fully incorporated.

In a separate bowl, whisk together the all-purpose flour, cornstarch, baking powder, baking soda, and salt. Gradually add this dry mixture to the wet ingredients while mixing on low speed.

Gently fold in both the semi-sweet and milk or white chocolate chips and any optional nuts.

Divide the dough into 8-10 large balls, making sure not to flatten them.

Preheat your oven to 400°F (205°C). Line a baking sheet with parchment paper and place 3-4 dough balls onto the sheet. Bake for 9-11 minutes.

Allow the cookies to cool on the pan for about 10 minutes before transferring them to a wire rack.