Preparation Steps

• In the bowl of your stand mixer fitted with the paddle attachment, beat together the cold cubed butter, brown sugar, and granulated sugar on medium speed for 3 minutes until light and fluffy. Add the eggs, vanilla extract, kosher salt, cocoa powder, corn starch, and baking soda. Mix on medium speed for 1 minute until smooth and fully combined, scraping down the sides and bottom of the bowl as needed.
• Turn the mixer to low speed and gradually add the flour, mixing until just combined. Do not overmix. Use a rubber spatula to stir in the semi-sweet chocolate chips by hand until evenly distributed throughout the dough. Chill the dough for 15 minutes in the refrigerator.
• While the dough chills, preheat your oven to 400°F (200°C). Line a large baking sheet with parchment paper and set aside.
• Portion the dough into 1/3 cup (about 4.5-ounce) mounds. Arrange 4 mounds per baking sheet, leaving plenty of space for spreading. Bake for 9 to 11 minutes, until the edges are set and the surface appears dry with light cracking. The centers should still feel soft—this ensures they stay chewy!
• Let the cookies cool on the baking sheet for 4 minutes before transferring them to a wire rack to cool completely. Repeat with remaining dough. Enjoy slightly warm or at room temperature for maximum fudginess.