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Preheat the oven to 350°F. Lightly grease a 9" x 13" pan. If you plan to turn the whole sheet of Fudge Brownies out of the pan at once, grease the pan, line it with parchment, and grease the parchment.
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In the bowl of a stand mixer fitted with the flat beater attachment or in a large bowl working with an electric hand mixer, combine the eggs, cocoa, salt, baking powder, espresso powder, and vanilla. Beat on medium speed for about 1 minute, or until combined and mostly smooth; the mixture will be quite thick.
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In a saucepan set over low heat or in a medium-sized microwave-safe bowl, melt the butter, then add the sugar and stir to combine. Continue to heat (or microwave) the mixture briefly, just until it's hot (about 110°F to 120°F), but not bubbling; it'll become shiny as you stir. Heating the mixture to this point will dissolve some of the sugar, which will help produce a shiny top crust on your brownies.
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Add the hot butter/sugar mixture to the egg/cocoa mixture, stirring until smooth. (A dough whisk is a helpful tool here.)
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Add the flour and chocolate chips, stirring until smooth. Be sure to scrape the sides and bottom of the bowl to incorporate all the ingredients.
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Transfer the batter to the prepared pan and spread it into an even layer, smoothing the top.
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Bake the brownies for 28 to 32 minutes, until the edges feel set and the center looks moist but not uncooked. When testing to see if brownies are done, take a toothpick or the tip of a sharp knife and carefully poke it into the center of the pan, digging around just enough to see the interior. You should see moist crumbs, but no uncooked batter. Yes, you'll be left with a small divot in the center of your brownies; just cut around it when you're cutting the brownies into squares — baker's treat!
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Remove the brownies from the oven and cool on a rack before cutting and serving.
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Store any leftover Fudge Brownies, well-wrapped, at room temperature for 5 to 6 days. Freeze for longer storage.
