Preparation Steps

• In a large mixing bowl, use a hand mixer to combine the brown sugar, granulated sugar, and softened butter. Mix until light and creamy.
• Add the egg, egg yolk, and vanilla extract. Mix until fully incorporated and smooth.
• In a separate medium bowl, whisk together the flour, cocoa powder, baking powder, salt, and baking soda.
• Gradually add the dry ingredients into the wet ingredients, mixing on low speed until just combined. Be careful not to overmix.
• Divide the dough into three equal portions. Wrap each portion tightly in plastic wrap and refrigerate for 30 minutes.
• Once the dough has chilled, preheat oven to 350°F. Line a baking sheet with parchment paper. Set aside.
• After chilling, place a large sheet of parchment paper on your work surface. Unwrap one portion of dough and roll it out into an 8-inch square about 0.25 inch thick. Sprinkle 1/3 of the chocolate chunks evenly over the surface, gently pressing them in.
• Unwrap the second portion of dough and roll it out separately into a square about the same thickness. Carefully lay it on top of the chocolate-covered first layer. Press down gently.
• Sprinkle 1/3 of the chocolate chunks over the second layer, pressing them in slightly.
• Roll out the final portion of dough and place it on top to form a three-layer dough stack. Tuck any loose chocolate chunks back into the dough as needed.
• Gently roll the entire stack with a rolling pin until it forms a 10-inch square about 0.5 inch thick.
• Top with the remaining chocolate chunks.
• Use a sharp knife to cut the dough into 2-inch squares (approximately 25 cookies). Place the squares on the lined baking sheet, spacing them about 1 inch apart.
• Bake for 11–14 minutes, or until the edges are set and the centers no longer appear wet.
• Let the cookies cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely.