Preheat the Oven: Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper to ensure your cookies don’t stick.
Cream the Butter and Sugars: In a large mixing bowl, beat the softened butter, light brown sugar, and granulated sugar using a hand mixer or stand mixer on medium speed until the mixture is light and fluffy. This should take about 2-3 minutes.
Add the Egg and Vanilla: Add the large egg and pure vanilla extract to the butter-sugar mixture. Beat until well combined.
Mix Dry Ingredients: 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, mixing until just combined.
Fold in the Chocolate Chips and Walnuts: Gently fold in the semi-sweet chocolate chips and chopped walnuts using a spatula. Make sure they are evenly distributed throughout the dough.
Scoop the Dough: Using a cookie scoop or tablespoon, scoop the cookie dough onto the prepared baking sheet, leaving some space between each cookie to allow for spreading.
Bake the Cookies:
