Preheat the Oven and Prepare Baking Sheets

Preheat your oven to 350°F (175°C). Line baking sheets with parchment paper or silicone baking mats.

Mix the Wet Ingredients

In a large mixing bowl, combine the melted butter, brown sugar, and granulated sugar. Beat together until smooth. Add the egg, egg yolk, and vanilla extract, and mix until well combined.

Combine the Dry Ingredients

In a separate bowl, whisk together the flour, baking soda, cornstarch, and salt.

Add the Dry Ingredients to the Wet Ingredients

Gradually add the dry ingredients to the wet ingredients, mixing on low speed just until combined. Be careful not to overmix, as this can make the cookies tougher.

Fold in the Chocolate Chips

Using a spatula, gently fold in the chocolate chips until evenly distributed throughout the dough.

Chill the Dough (Optional)

For thicker cookies, cover and refrigerate the dough for 30 minutes. This step is optional but helps create a chewier texture.

Scoop and Shape the Cookies

Drop rounded tablespoons of cookie dough onto the prepared baking sheets, spacing them about 2 inches apart.

Bake the Cookies

Bake in the preheated oven for 10-12 minutes, or until the edges are golden and the centers look slightly underbaked. They’ll firm up as they cool, giving them that perfect chewy center.

Cool and Serve

Allow the cookies to cool on the baking sheets for 5 minutes, then transfer them to a cooling rack to cool completely.