In a large bowl using an electric mixer, mix together boxed cake mix, water, oil, eggs, baking soda, and baking powder on medium speed, about 2 minutes. Mixture should be combined and smooth. Add bananas; mix until combined.
Scoop batter into cupcake liners, no more than ⅔ full or use a #24 disher. Bake for about 12-15 minutes. Check cupcakes around 13 minutes to avoid over-baking. Insert a toothpick into the center of the cupcake, if it comes out clean it is done.
Remove cupcakes from oven and allow cupcakes to cool in cupcake pan for 4 minutes; transfer to wire rack and cool completely. Cupcakes should be cooled completely before frosting.
For Buttercream Frosting
In a large bowl using an electric mixer, cream butter and shortening until creamy and smooth. Add vanilla and butter extracts; mix until combined.
Turn mixer on lowest speed and slowly add 1 lb of powdered sugar; mix until creamy. Scrape down bowl as necessary. Adding the powdered sugar gets dusty - place a damp towel over the top of the mixer to shield flying powdered sugar dust.
Continue to slowly add remaining powdered sugar; blend until completely combined.
Once all powdered sugar has been mixed in, add 1 tablespoon of milk at a time and mix. Continue to add and mix until desired consistency is achieved.
Decorate Very Banana Cupcakes. Eat & Enjoy!
Notes
Store Very Banana Cupcakes in an airtight container. Cupcakes will keep for 4+ days.¹ For a creamy buttercream use pure cane sugar powdered sugar. If it doesn't say "pure cane sugar" it is beet sugar, which can leave buttercream gritty.² Pure non-clear vanilla extract can be used instead of clear vanilla extract; however, this will affect the color of the buttercream. It will make it less white.³ Butter vanilla adds more butter flavor to the buttercream; it is subtle and worth adding but is not necessary.