1. Preheat oven to 350 degrees. Grease a 9x13 pan.
2. Beat together eggs, cocoa, baking powder, espresso powder and vanilla until smooth.
3. Melt the butter in the microwave in a small microwave-safe bowl.
4. Add the sugar to the melted butter and combine. Microwave mixture in about 10-15 second increments, mixing each time, until the mixture is hot (about 110-120 degrees), but not bubbly. It should take on a shiny look when it's ready. Heating this mixture will dissolve more of the sugar and give a shiny crust on top of the brownies. You could also do this step in a saucepan over low heat.
5. Add the butter mixture to the eggs mixture and mix until smooth
6. Microwave the chocolate chips in about 20 second increments until fairly soft, but not totally melted.
NOTE: If you want them to be completely incorporated, melt them completely. If you want them to be chunks in the brownies, do not microwave them.
7. Add flour and chocolate chips to batter and mix until smooth.
8. Pour batter into pan and bake for about 30 minutes, or until toothpick comes out with just a few moist crumbs.
9. When done, remove from oven and allow to cool.