Prep Your Pan and Oven: Preheat your oven to 350°F (175°C). Line an 8×8 inch metal baking pan with parchment paper, leaving an overhang on two sides to act as a “sling.”

Melt Butter and Sugars: In a large, microwave-safe bowl, melt the butter. Whisk in the granulated and brown sugars until fully combined.

Whisk in Eggs and Vanilla: Add the eggs and extra egg yolk, one at a time, along with the vanilla extract. Whisk vigorously for about 1-2 minutes until the mixture becomes thick, pale, and glossy. This step is crucial for creating that crackly top!

Fold in Dry Ingredients: Add the flour, cocoa powder, espresso powder, and salt to the bowl. Switch to a rubber spatula and gently fold until just combined. You want to see a few streaks of flour remaining.

Add Chocolate Chips: Pour in the chocolate chips and fold a few more times until the flour streaks disappear. Be careful not to overmix!

Bake to Perfection: Pour the batter into your prepared pan and spread it into an even layer. Bake for 30-35 minutes. A toothpick inserted into the center should come out with moist, fudgy crumbs attached, but not wet batter.

Cool Completely: This is the hardest part! Let the brownies cool completely in the pan on a wire rack for at least 2 hours before cutting.