Start by preheating your oven to 350°F (175°C). Lightly spray an 8×8-inch pan, then line it with parchment paper, leaving some overhang to help lift the brownies out easily.
Place 1 cup of chocolate chips and butter in a microwave-safe bowl, then melt them together. Heat in 30-second bursts, stirring each time until smooth and glossy.
Stir in both sugars and let the mixture cool slightly, this keeps the eggs from cooking when added. Whisk in the eggs and vanilla until the batter thickens and looks like rich chocolate pudding.
Add the cocoa powder, cornstarch, espresso powder, and salt, then stir until smooth. The cornstarch ensures these brownies remain delightfully fudgy without the need for flour.
If you like extra chocolate, fold in some of the remaining chips. Pour the batter into your pan, spread evenly, then sprinkle the rest of the chips on top for that classic bakery touch.
Bake for 25 minutes, checking for a toothpick that comes out with moist crumbs, no raw batter, but not completely clean either.
Leave the brownies in the pan to cool a little bit. Enjoy!