In a large mixing bowl, cream together the softened butter, brown sugar, and granulated sugar using a mixer until light and fluffy. This step helps to incorporate air, giving your cookies a soft texture.

Add the egg to the mixture and beat until fully combined, creating a smooth and creamy batter.

In a separate bowl, whisk together the all-purpose flour, cornstarch, baking soda, baking powder, and a pinch of salt. This ensures the dry ingredients are evenly distributed.

Gradually add the dry ingredients to the wet mixture, mixing on low speed or by hand until just combined. Avoid over-mixing, as it can result in tougher cookies.

Fold in the chocolate chips and chopped chocolate gently, making sure they’re evenly distributed throughout the dough.

Cover the bowl with plastic wrap and refrigerate the dough for at least 30 minutes. Chilling prevents excessive spreading and enhances the cookie flavor.

Preheat your oven to 350°F (175°C) while the dough chills. Line a baking sheet with parchment paper or a silicone baking mat to prevent sticking.

Scoop rounded portions of the chilled dough onto the prepared baking sheet, leaving about 2 inches between each cookie. Flatten slightly for a more Levain-inspired look.

Bake in the preheated oven for 10-12 minutes, or until the edges are golden brown and the centers look slightly underbaked. This ensures a soft, gooey texture.

Remove the baking sheet from the oven and let the cookies cool for 5 minutes. Transfer to a wire rack to cool completely before serving.