Preheat oven to 350 degrees and spray cake pans with pam baking spray, set aside

Using a standing mixer, beat together the cake mix, eggs, milk and butter until smooth and combined

Split the batter between the 3 pans and bake for 25 -30 minutes or until a toothpick comes out clean

Using a standing mixer, beat all ingredients until combined, smooth and stiff peaks form

Scoop about 1 1/2 C frosting into the piping bag and set aside

Using the cake leveler, cut the domes off the cake rounds to make them leveled

Place one cake round onto the cake board

Scoop 1 1/2 C of the chocolate frosting onto the top of the cake and smooth evenly with the angled spatula

Place another cake round on top of the first one

Scoop another 1 1/2 C of the chocolate frosting onto the second cake round and smooth evenly

Place the third cake round on top of the second one

Scoop remaining chocolate frosting onto the top of the cake and frost entire cake

Place cake on a cake stand in the middle of a cookie sheet

Sprinkle some of the rainbow sprinkles around the bottom of the cake

Place cake into the fridge for an hour to allow the frosting to firm up

Pipe dollops of chocolate frosting along the top of the cake

Place a piece of cosmic brownie in between the chocolate frosting

Sprinkle some more rainbow sprinkles around the top

Cut into slices and enjoy!