Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper. Set your eggs out now if they’re cold, because room temperature eggs blend more smoothly and help the dough come together faster.

In a medium bowl, whisk together the flour, cocoa powder, baking soda, and salt until the cocoa is fully blended in and the mixture looks evenly chocolate-colored. If your cocoa powder is lumpy, sift it first so the dough doesn’t end up with dry pockets.

Melt the chopped semi-sweet chocolate in a microwave-safe bowl in 15-second bursts, stirring between each round, until completely smooth. Let the melted chocolate sit for 3 to 5 minutes so it cools slightly. You want it warm and pourable, not hot.

In a large bowl, beat the softened butter, granulated sugar, and brown sugar for 3 to 4 minutes until the mixture looks pale, fluffy, and creamy. Scrape down the sides of the bowl halfway through so everything mixes evenly.

Add the eggs in two additions, mixing well after each one. Add the vanilla and mix again until smooth. The mixture should look glossy and thick, not runny.

Pour the melted chocolate into the bowl and mix until fully blended. The batter should darken immediately and look shiny and rich, almost like brownie batter at this stage.

Add the dry ingredient mixture and mix on low speed just until the flour disappears and a thick dough forms. It should look scoopable and thick, not wet or pourable. Stop mixing as soon as you no longer see dry flour.

Add the dark chocolate chunks and mix briefly just until the chunks are evenly distributed. Switching to a spatula here helps prevent overmixing and keeps the dough thick.

Cover the dough and chill for 45 minutes. This is what gives you thick cookies with chewy centers instead of thin, spread-out cookies.

Scoop the dough into 2-tablespoon portions and place them on the prepared baking sheets about 2 inches apart. Bake for 11 to 13 minutes until the edges look set and the centers still look slightly soft. The cookies will continue to bake on the hot tray after you remove them.

Let the cookies cool on the baking sheet for 10 minutes, then transfer to a wire rack to cool completely. Once cooled, the edges will be slightly crisp and the centers will stay chewy and fudgy.