Preheat oven to 375°F.
In a small bowl, mix milk and apple cider vinegar. Set aside.
In a large bowl, mash 3 bananas (save 1 banana for topping).
Add sugar, oil, maple, and vanilla to the bananas, and mix together, using a whisk.
Add the milk-vinegar mixture and mix well.
Add flour, baking soda and spices and combine all together – making sure not to over mix it – just until the flour is combined.
If you are adding walnuts and/or chocolate chips, fold them into the batter gently.
Grease a loaf pan.
Pour in the batter.
Slice the extra banana and place the banana slices on top of the batter. Sprinkle a bit of cinnamon on top.
If you’d like, sprinkle with extra walnuts and/or chocolate chips.
Bake for 45 minutes.