Preheat oven to 410°F (210°C). Line baking sheets with parchment paper.
In a large bowl, cream together the cold butter, granulated sugar, and brown sugar until well combined.
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
In a separate bowl, whisk together the flour, cornstarch, baking powder, baking soda, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Fold in the chocolate chips and nuts (if using) until evenly distributed.
Using an ice cream scoop or your hands, form dough into large balls (about 6 oz each) and place them on the prepared baking sheets.
Bake in the preheated oven for 10-12 minutes, or until the edges are golden but the centers are still soft.
Let the cookies cool on the baking sheets for 10 minutes before transferring to a wire rack to cool completely.
Enjoy these delicious Levain Bakery-inspired cookies with a glass of milk!
Prep Time: 20 minutes | Baking Time: 10-12 minutes | Total Time: Approximately 1 hour | Servings: 12 large cookies