In a mixing bowl, add the eggs, cocoa, salt, baking powder, espresso powder and vanilla. Beat at medium speed for about 4 minutes.
Melt the butter and sugar in a saucepan over low heat until the mixture becomes shiny, but not bubbly, about 110°F/120°F.
Pour the hot butter/sugar mixture into the egg/cocoa mixture and mix on low speed until smooth.
Add the flour and mix until smooth.
At this point, turn the oven to 350°F and lightly grease a 9" x 13" pan.
Wait at least 20 minutes* and then gently fold in chocolate chips.
Spoon the batter into the greased pan.
Bake for about 35-38 minutes, or until a tester (fork, knife, toothpick) inserted into center comes out clean. Brownies should be set on the edges and the center should be very moist, but not raw.
Let cool before cutting.
Notes
Heating the butter/sugar to 110°F/120°F will produce a shiny, flaky top crust. *If you want the chocolate chips to melt into the brownies, don't wait the 20 minutes and preheat the oven at the start of the preparation.