Melt Chocolate & Butter
In a microwave safe bowl, melt chocolate and butter together in 30-second bursts, stirring until smooth. Set aside to cool slightly.
Whisk Dry Ingredients
In a medium bowl, whisk together flour, cocoa powder, baking powder, and salt.
Beat Eggs & Sugar
In a large bowl, use a hand mixer to beat eggs, brown sugar, and granulated sugar until thick and pale (about 3 minutes). Mix in vanilla and espresso powder.
Combine Wet & Chocolate Mixture
Slowly pour the melted chocolate into the egg mixture, mixing on low until combined.
Add Dry Ingredients
Gently fold in the flour mixture until just combined. The batter will look like glossy brownie batter.
Add Chocolate Chips
Stir in chocolate chips (and nuts if using).
Chill the Dough
Cover the bowl and refrigerate for 30 minutes. This step prevents spreading and gives cookies their chewy texture.
Scoop & Bake
Preheat oven to 350°F (175°C).
Line a baking sheet with parchment paper or a silicone mat.
Scoop dough (about 2 tablespoons each) onto sheets, spacing 2 inches apart.
Bake for 10–12 minutes, until tops are shiny and crackly.
Cool & Sprinkle
Let cookies cool on the sheet for 5 minutes before transferring to a rack.
Sprinkle lightly with flaky sea salt.