Step 1

Preheat the oven to 350 degrees Fahrenheit. Line the 8-inch square pan aluminum foil, leaving an overhang on the sides. Grease foil with cooking spray or butter.

Step 2

Place bittersweet and unsweetened chocolates and butter in a microwave-safe bowl and microwave on 70% power for 1 minute and stir. Microwave at 30-second intervals and stir until chocolate is completely melted. Stir in espresso powder and salt. Set aside.

Step 3

In a large bowl, beat eggs and sugar on high speed or until thick and pale yellow, for about 3 minutes. Add the melted chocolate and beat on low speed until well-combined.

Step 4

Gradually sift in the flour and whisk gently just until streaks of flour disappear.

Step 5

Pour batter into the prepared pan and bake for 40 minutes, or until a toothpick inserted into the center comes out with dry crumbs.

Step 6

Cool the brownies in the pan for 5 minutes. Lift the brownies out of the pan using the overhang and transfer them onto a wire rack to cool completely. Slice and enjoy!