Step 1

In a large bowl, whisk together the flour, cocoa powder, baking soda, cornstarch, and salt. Set aside.

Step 2

In a separate, microwave-safe bowl, combine the chopped semi-sweet chocolate and one stick of unsalted butter. Loosely cover and heat for 20 seconds. Stir, then microwave for another 15 seconds. Stir until smooth. Mix in the sugars until mostly dissolved, and then let cool to room temperature.

Step 3

Once cooled, mix the eggs and vanilla extract into the chocolate mixture. Add the wet mixture to the dry ingredients and fold in until well-combined (you may need to use your hands to work the mixture together towards the end).

Step 4

Work in 1 cup of the chocolate chunks. Cover the dough and refrigerate for 30 minutes.

Step 5

Preheat the oven 325 degrees F. Line two baking sheets with parchment paper.

Step 6

Roll the dough into ping pong ball sized spheres. Place the spheres on the prepared baking sheets and press down on the tops gently with the palm of your hand. Place one baking sheet in the oven and bake the cookies for 15 minutes, or until spread out, cracked, and just beginning to stiffen on the edges. Remove the cookies from the oven and press additional chocolate chunks in the top while they’re still hot and soft. Let cool on the baking sheet for 10-15 minutes, or until set enough to remove from the baking sheet. While that batch cools, add the second baking sheet to the oven and repeat until all of the cookies have been baked.