Step 1

Preheat the oven to 350°F. Lightly grease a rimmed half sheet pan (about 13" x 18" outside dimensions).

Step 2

, Crack the eggs into a large bowl; the bowl of your stand mixer works well here. Add the cocoa, salt, baking powder, espresso powder, and vanilla. Beat slowly until everything is barely combined, then beat at medium speed for about 1 minute, or until smooth.

Step 3

, In a medium-sized microwave-safe bowl, or in a saucepan set over low heat, melt the butter. Add the sugar and stir to combine. Continue to heat (or microwave) 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.

Step 4

, Add the hot butter/sugar mixture to the egg/cocoa mixture, stirring until smooth.

Step 5

, Add the flour and chips, again stirring until smooth.

Step 6

,  Spoon the batter into the prepared pan, smoothing the top as best you can.

Step 7

, Bake the brownies for 30 to 35 minutes, until the edges feel set and the center is very moist, but not uncooked. A knife tip poked into the center shouldn't reveal any raw batter.

Step 8

, Remove the brownies from the oven and cool them on a rack before cutting and serving.

Step 9

, Store any leftovers, well-wrapped, at room temperature for five to six days; freeze for longer storage.