In a medium bowl, whisk together the cocoa powder, salt, and baking powder.
Add the eggs and vanilla and whisk until very smooth. Set aside.
In a small saucepan melt 1/2 cup butter until the butter starts to foam. Add the sugar and stir until the sugar is melted.
Add the hot butter mixture to the cocoa mixture. Whisk until smooth. Stir in the flour and then stir in 1/2 cup of chocolate chips until they melt. Let cool for 15 minutes.
While the batter is cooling, preheat oven to 350 degrees. Butter an 8x8 inch baking dish and line with parchment paper.
Once the batter has cooled, stir in the final cup of chocolate chips. Spoon the batter into the prepared baking pan. Spread it out evenly.
Bake for about 25 minutes or until a toothpick inserted in the center comes out with a few moist crumbs. The edges will be set, but the center will still look a little moist. Let cool before cutting into squares.