Preheat oven to 350*F and lightly grease a 9"x13" pan. If desired, line bottom of pan with parchment paper.
In a large bowl, add 4 eggs, and beat with cocoa, salt, baking powder, espresso powder and vanilla. Stir until fully combined and smooth.
In a medium sized bowl, melt butter in the microwave (or melt in a small sauce pan on the stove). When melted, add sugar, and stir to combine.
Add warm butter/sugar mixture to the egg/cocoa mixture, stiring until smooth. Make sure the butter mixture is warm, but not too hot, or it will scramble your eggs.
Add the flour and chocolate chips to batter and stir until fully incorporated.
Spread batter into prepared pan, and smooth as needed.
Bake brownies about 30 minutes. Test for doneness by inserting a toothpick in the center of the brownies and making a little divit so you can see the center a bit. You should find moist crumbs, but no wet batter.
Cool pan on wire cooling rack.