Pour the cake mix into a large bowl, then remove all of the lumps by sifting or whisking.
Add in the milk, vegetable oil, and eggs.
Mix until the batter is smooth.
Toss in the bananas pieces into the batter, then fold in.
Spray two 9 inch cake pans with baking spray or add parchment paper at the bottom of the pans.
Pour the cake batter into both cake pans.
Bake the cakes in the oven on 350 F for 25 minutes, or until done.
Let the cakes cool completely.
Combine the ingredients for the vanilla buttercream, and mix until creamy.
Once the cakes are completely cool, frost them ( watch the video).
Add vanilla wafers on the cake.
Let sit for at least 1 hour.
Serve & enjoy!