1. Melt your butter in a microwave-safe bowl or a small pot on the stove. Let it cool down for a few minutes so it doesn’t cook the eggs.

2. In a separate medium bowl, whisk together the flour, cocoa powder, baking soda, and salt. Set aside.

3. Pour the cooled, melted butter into a large mixing bowl. Add both the brown sugar and white sugar and whisk vigorously for about a minute until smooth.

4. Add the two large eggs and the extra egg yolk one at a time, whisking until the batter is light and glossy. Stir in the vanilla extract.

5. Gently pour the dry ingredients into the wet mixture. Use a rubber spatula to fold everything together until just combined. Do not overmix.

6. Fold in the chocolate chunks or chips, reserving some to press onto the tops of the cookies if desired.

7. Cover the bowl with plastic wrap and chill the dough in the refrigerator for at least 3 hours, or overnight for best results. This step is essential.

8. When ready to bake, preheat the oven to 350°F (175°C). Line two large baking sheets with parchment paper.

9. Use a medium cookie scoop (about 2 tablespoons) to portion the chilled dough into balls, placing them about 2 inches apart on the baking sheets.

10. Bake for 10-12 minutes. The edges should look set, but the centers will still appear soft. Let them cool on the baking sheet for 5-10 minutes before moving to a wire rack.