Prep the oven: Preheat oven to 350°F. Line two baking sheets with parchment paper and use cool pans for each batch.
Melt chocolate and butter: Melt butter and chopped chocolate in 20-second bursts, stirring until smooth. Let cool slightly.
Beat eggs and sugars: Beat eggs, granulated sugar, and brown sugar for 3–5 minutes until pale, thick, and glossy. Mix in vanilla.
Add melted chocolate: Slowly pour the cooled chocolate mixture into the egg mixture. Mix on low until smooth and glossy.
Fold in dry ingredients: Whisk flour, cocoa powder, baking powder, salt, and espresso powder if using. Fold into the wet mixture until just combined.
Add chocolate chips: Fold in chocolate chips or chopped chocolate. Save a few pieces to press on top if desired.
Scoop and bake: Scoop 1 1/2 to 2 tablespoon portions onto baking sheets, spacing them 2–3 inches apart. Bake for 10–12 minutes, until tops crack and edges set.
Cool before serving: Let cookies cool on the baking sheet for 5–10 minutes, then transfer to a wire rack. Cookies will firm up as they cool.
