Prepare the pan and oven. Line two baking sheets with parchment paper and set your oven to 350°F (175°C). Let it fully preheat while you make the dough.

Melt chocolate and butter. In a heatproof bowl, combine 1 cup chocolate and 4 tablespoons butter. Microwave in 20–30 second bursts, stirring between each, until smooth and glossy. Set aside to cool for 5 minutes. You want it warm, not hot.

Whisk sugars and eggs. In a separate bowl, whisk granulated sugar, brown sugar, and eggs for about 30–45 seconds until slightly thick and well combined. Mix in the vanilla.

Combine wet ingredients. Slowly pour the melted chocolate mixture into the egg mixture, whisking as you go. This keeps the eggs from curdling and gives you that shiny, brownie-like batter.

Mix the dry ingredients. In another bowl, whisk together the cocoa powder, flour, baking powder, salt, and espresso powder (if using). Break up any cocoa clumps with your whisk.

Bring it all together. Fold the dry ingredients into the chocolate mixture with a spatula. Stop as soon as you no longer see dry streaks. If you’re adding extra chocolate chips, fold them in now.

Rest the batter. Let the batter sit at room temperature for 10–15 minutes. It will thicken to a soft, scoopable consistency. This helps the cookies keep their shape and develop crackly tops.

Scoop and top. Use a cookie scoop or tablespoon to portion dough into mounds, about 1.5 tablespoons each, spacing them 2 inches apart. If you like, press a few extra chips on top and sprinkle a pinch of flaky sea salt.

Bake. Bake one sheet at a time for 9–11 minutes, until the tops are shiny and cracked, and the edges look set. The centers should still look slightly soft—that’s the secret to fudgy cookies.

Cool. Let cookies cool on the baking sheet for 5–10 minutes before transferring to a rack. They will firm up as they cool but stay chewy inside.