Preheat the oven to 350 degrees F and line a 9x9 inch square pan with parchment paper.

Start by making the brown butter. In a small saucepan, heat 200g of unsalted butter over medium heat for several minutes, swirling to even out the color. The butter will be ready once the fat solids have separated and darkened, and the butter is an even medium amber color.

Weigh out 170g of the brown butter in a large bowl. If you are short a few grams, just add regular unsalted butter to make up the difference. 

Add the brown sugar, granulated sugar, and chocolate to the brown butter. Heat the mixture in the microwave in 20 second increments until the sugars and chocolate are fully melted. Whisk the mixture until smooth. 

Add the eggs to a separate small bowl and briefly beat them to break up the yolks. Add the eggs to the butter, sugar, chocolate mixture, and whisk until fully combined. Whisk in the vanilla.

Next, fold in the flour, cocoa powder, espresso powder, and salt until just combined. 

Fold in the finely chopped chocolate.

Pour the batter into the prepared pan and bake the brownies for 33-36 minutes or until a toothpick inserted comes out clean. Allow brownies to cool completely in the pan before removing and cutting.