Cream together butter and sugar until a smooth paste is created
Add in one egg at a time, allowing to fully incorporate
Add in bananas and vanilla. Mix until bananas are smooth and incorporated. Mix may look broken. This is ok.
Whisk together flour, baking powder and soda along with the salt
Gently mix or fold dry ingredients into the wet ingredients until batter forms
Add in sour milk and mix until incorporated and batter is smooth
Place in greased and sugared pan
Bake in preheated 350°F oven on center rack for 50-65 minutes or until just firm to touch