Directions - Preheat oven to 325FMix together butter, oil, sugars and eggs.Add mashed bananas, sour cream and vanilla, stirring together well.Mix in flour, baking soda , baking powder, chocolate chips (and nuts if desired) and salt, stirring until it is well blended.Pour into 1 greased large loaf pan.Sprinkle additional brown sugar generously over top of batter, using your hand to gently pat some of it into the batter.Bake at 325 degrees: large loaf pan for about 1 to 1 1/2 hours , smaller loaves for about 45 minutes. ( check with toothpick to see if done)Allow bread to cool in pans for about 20 minutes, then run a sharp knife around the edges, tap the pan on the counter several times to release the bread from the bottom of the pan, then invert pan over a wire rack and let the bread fall onto the rack to finish cooling completely (which never happens in my house....the cool completely doesn't exist because it is swooped down upon by the "man" vultures and gone in 60 seconds)