Preheat the oven to 350 degrees F.
Mix cocoa and boiling water until smooth and let cool to room temperature.
In a different bowl, mix eggs, 1/4 of the room temp cocoa mixture, and vanilla until combined.
Separately, mix flour, brown sugar, baking powder, baking soda, and salt in a large mixing bowl on low speed. Add butter and the rest of the cocoa mixture.
Once the dry ingredients are moistened, increase the speed to medium and mix for 1-2 minutes. Remember to scrape down the sides of the bowl periodically to insure the ingredients are properly combined.
Slowly add in egg mixture a bit at a time.
Pour batter into the greased cake pans, dividing the batter evenly. It's also helpful to put a sheet of parchment paper in the pans to prevent sticking.
Bake for 25-30 mins or until a toothpick inserted into the center is smooth when removed.
Allow to cool to room temperature on cooling racks before frosting.