Mash banana in a small bowl and stir in a couple drops of lemon juice to prevent browning.
In the stand mixer with the paddle attachment, cream the butter on high speed until light and fluffy.
Add the banana into the mixer and mix until combined.
Add four cups of powdered sugar and vanilla extract into the mixer. Mix on low speed until well combined.
If the frosting is separating or too thin, mix in up to two more cups of powdered sugar until the frosting comes together smoothly.