Make the brownies:

• Pre heat oven to 350°. Lightly grease, or line with non-stick foil, a 9” x 13” brownie or cake pan.
• Whisk together the flour, cocoa powder and salt in a small bowl. Set aside.
  1 cup flour, ¼ cup cocoa powder, 1 teaspoon salt
• Place the dark chocolate, unsalted butter, and espresso powder in a large microwave safe bowl. If your microwave has a chocolate melting feature, use that, otherwise, heat for 1 minute in the microwave, stir and then continue to heat in 30 second intervals, stirring after each interval just until the chocolate is fully melted. This can also be done over a double boiler.
  12 ounce dark chocolate, 1 cup unsalted butter, 1 teaspoon espresso powder
• While the chocolate and butter are melting, whisk the eggs, sugar and brown sugar until thick and ribbony (this is faster with an electric mixture, but can be done by hand). Whisk in the vanilla until combined.
  1 cup sugar, 1/2 cup brown sugar, 5 eggs, 1 tablespoon vanilla
• Whisk the chocolate mixture into the egg mixture until a homogenous, glossy mixture is achieved. At this point the sugar should be fully dissolved with no grittiness in the mixture.
• Stir in the flour and cocoa powder just until the flour disappears. Fold in the chocolate chips, or your favorite mix-in(s).
• Pour the batter into the prepared pan, smooth out the top.
• Place the pan in the pre-heated oven and bake for about 35 minutes. The top will appear set, the edges slightly puffed and possibly a crack or two in the surface.
• Allow to cool completely before cutting into 24 large bars or 40 small bars. Store in an air-tight container at room temperature.