In a medium mixing bowl, whisk together the all-purpose flour, baking soda, baking powder, salt, and cornstarch until everything is evenly combined.

Set the bowl aside while preparing the butter mixture.

In a large mixing bowl, beat the softened butter, brown sugar, and granulated sugar together using an electric mixer for about 3–4 minutes.

The mixture should become light, fluffy, and creamy. This step incorporates air into the dough, giving the cookies their tender texture while helping them bake evenly.

Avoid rushing this step, as properly creamed butter creates a softer cookie.

Beat in the eggs one at a time, mixing well after each addition.

Add the vanilla extract and continue mixing until the batter becomes smooth and creamy.

Scrape down the sides of the bowl with a rubber spatula to ensure everything is fully incorporated before moving on.

Gradually add the prepared dry ingredients into the butter mixture while mixing on low speed.

Mix only until no dry flour remains. Overmixing develops gluten, which can make cookies tougher instead of soft and chewy.

Fold in the chocolate chips and optional chocolate chunks using a rubber spatula until evenly distributed throughout the dough.

Cover the bowl with plastic wrap and refrigerate the cookie dough for 30–60 minutes.

Chilling helps prevent the cookies from spreading too much while baking and creates a thicker, bakery-style cookie with a chewy center.

If you’re short on time, even a 20-minute chill will improve the texture.

Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper.

Using a medium cookie scoop or about 2 tablespoons of dough, scoop evenly sized portions onto the prepared baking sheets, leaving approximately 2 inches of space between each cookie to allow for spreading.

Bake for 10–12 minutes, or until the edges are lightly golden while the centers still appear slightly soft. Avoid waiting for the centers to become fully firm, as they will continue cooking on the hot baking sheet after being removed from the oven.

Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.