Add half of your dry ingredients to the batter and mix until just combined. Do not overmix. Add your milk into the batter and mix until well combined. Mix in your remaining dry ingredients until well combined and smooth. Do not over mix.
Spread about 1 cup of your frosting into an even layer on top of one of you cakes. Add the second layer of cake on top of the frosting. Spread another cup of frosting on top of that cake and spread into an even layer.