Method
Preparation
Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a large bowl, beat the cold cubed butter, brown sugar, and granulated sugar together until creamy and smooth.
Beat in the cold eggs one at a time, mixing until well incorporated.
In another bowl, whisk together the all-purpose flour, cornstarch, baking powder, baking soda, and salt until well combined.
Gradually add the dry mixture to the wet mixture, stirring with a spatula until just combined. Do not overmix!
Gently fold in the semi-sweet chocolate chips, milk or white chocolate chips, and any optional nuts or espresso powder.
Using a large cookie scoop, drop dough balls onto the prepared baking sheet, spacing them about 2 inches apart.
Baking
Bake for 12-15 minutes, or until the edges are lightly golden but the centers are still soft.
Remove from the oven and let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.
Notes
You can substitute the butter with a plant-based alternative for a dairy-free version. Additionally, you can use coconut sugar in place of brown sugar for a different flavor profile. Adding a pinch of cinnamon or a sprinkle of sea salt on top before baking imparts extra flavor.