Preheat your oven to 180 degrees fanbake
Begin by adding the apple cider vinegar to the cup of milk and leave to turn sour and get chunky.
Mash the bananas with a fork.
Place all the wet ingredients, including the bananas and sour milk.
Add the chocolate chips, sugar and flour to the mixing bowl and gently combine.
Spoon equal amounts into muffin casings or a muffin tray.
Place in the oven and cook for 25-30 minutes