In a mixer, beat the butter and sugar.
Add the egg and vanilla.
Add banana and salt until combined.
Add the flour.
Pour into 8x8 pan lined with nonstick foil.
Bake at 350 for 27-30 minutes.
Let cool.
Frosting:
Put first 4 ingredients in the mixer and beat.
Add milk slowly until the desired consistency. (Thick but spreadable)