Preheat oven to 350 degrees. Butter and flour two 8 inch round cake pans, set aside.
In a stand mixer, using the paddle attachment, beat the butter and brown sugar on medium-high speed until it increases in volume and becomes fluffy, 3 to 5 minutes. Lower the mixing speed and add the eggs, one at a time, mixing until each egg is fully incorporated before adding the next.
In a medium sized bowl, combine the dry mix and cocoa powder.
With the mixer on low speed, add one fourth of the dry ingredients to the batter and mix until incorporated. Add half of the buttermilk and continue mixing until fully combined. Continue to alternate adding the rest of the dry ingredients and the buttermilk, scraping down the sides of the bowl if necessary.
Divide the batter evenly between the prepared pans and bake 40-45 minutes until the sides of the cake begin to pull away from the sides of the pan and a toothpick inserted in the center comes out clean.
Remove the pans from the oven and cool on a rack at least 15 minutes before inverting the cakes from the pans. Cool the cakes completely.
To decorate, place one of the cakes on a cake plate or stand. Tuck strips of parchment paper under the cake to keep the cake stand clean while decorating. Take 1 1/2 cups of the frosting and spread it evenly over the top of the cake. Place the second cake on top of the frosting, pressing down lightly. Insert a toothpick all the way into the cake on both sides to secure it.
Frost the cake completely, scooping half of the remaining frosting on top of the cake and spreading it down the sides and around, until the cake is completely frosted. Garnish with a sprinkle of the chopped chocolate chips.