Preheat the oven to 350°F. Lightly grease a 13x9 pan, line with parchment, and grease the parchment.
Crack 4 eggs into a bowl and whisk together with the cocoa, salt, baking powder, espresso powder, and vanilla for 1-3 minutes, or until smooth. Try to incorporate as little air as possible.
In a saucepan set over low heat, melt the butter, then add the sugar and stir to combine. Continue to heat briefly, just until the mixture is hot (about 110°F to 120°F), but not bubbling; it'll become shiny looking as you stir it.
Add the hot butter/sugar mixture to the egg/cocoa mixture, stirring until smooth.
Fold in the flour and chips, stirring until smooth. Do not overmix!
Spoon the batter into the pan, using a spatula to spread the batter evenly.
Bake the brownies for 28 to 32 minutes, until the edges feel set, and the center should look very 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 two inches from the edge of the pan. It should come out clean.
Remove the pan from the oven and use a paring knife or metal spatula to loosen the edges of the brownie from the pan. Cool completely before cutting and serving.
Store leftovers well-wrapped at room temperature for 5-6 days. Freeze for longer storage.