Preheat oven to 350 degrees. Line a 9" x 13" baking pan with parchment paper or lightly grease with butter.
Mix together eggs, cocoa powder, salt, baking powder, and vanilla extract, with your stand mixer or hand mixer until incorporated, there will be a few small lumps.
Set a glass bowl over a pot of boiling water, turn the heat to medium-low, place the butter in the bowl and melt. When the butter is completely melted slowly add in 8 oz of the chocolate chips, stirring until completely melted. Slowly mix in the sugar until fully combined. Add to the cocoa powder mixture. Mix until smooth and shiny.
Add both flours and mix until fully incorporated.
Pour mixture into the baking pan, spread evenly, sprinkle 4 oz of chocolate chips on top.
Bake for 30 minutes or until toothpick inserted in the center comes out clean with only a few moist crumbs clinging to it.
Let cook before serving.