In a medium saucepan over medium heat, melt ½ cup of unsalted butter until it turns golden brown and develops a nutty aroma, about 5 to 7 minutes.

Add 1 cup of semi-sweet chocolate chips to the warm browned butter and stir until melted and smooth, about 2 to 3 minutes.

In a separate large bowl, whisk together 1 cup of all-purpose flour, ½ cup of dark cocoa powder, 2 teaspoons of espresso powder, and ½ teaspoon of salt.

In another large bowl, beat together 2 large eggs, 1 cup of granulated sugar, and 1 teaspoon of vanilla extract until light and fluffy, approximately 2 minutes.

With the mixer on low speed, gradually drizzle the cooled chocolate-butter mixture into the egg mixture, mixing until just combined.

Pour the brownie batter into a parchment-lined 8x8-inch baking pan and bake at 350°F (180°C) for 30 to 40 minutes.

Once baked, let them cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.