Preheat oven to 350F and grease a 9 x 13 baking pan
Beat the eggs at medium speed with cocoa, salt, baking powder, espresso powder, and vanilla for one minute or until smooth
Add sugar to melted butter in saucepan and stir to combine. Continue heating until mixture is hot but not bubbling - about 110F - 120F. It should become shiny as you stir it
Add hot butter/sugar mixture to egg/cocoa mixture, stirring until smooth
Add flour and chocolate chips, stirring until smooth
Spoon batter into prepared pan and bake for 28 - 32 minutes, until tester inserted comes out clean or with just a few moist crumbs clinging to it. The brownies should feel set on the edges and the center should look very moist but not uncooked. Remove from oven and cool on rack before cutting and serving