Preheat the oven to 180 degrees/gas mark 4
Mash the bananas in a bowl with a fork
Add the milk, vegetable oil, vanilla extract and apple cider vinegar into the bowl with the banana and stir
Put the dry ingredients (brown sugar, flour, oats, baking powder, bicarbonate of soda, cinnamon, salt) in a separate bowl and mix together
Add the dry ingredients to the wet ingredients bowl. Stir gently until combined. Do not over mix! When all the ingredients are nearly combined add the blueberries and stir them in lightly.
Spoon the mixture into muffin cases and sprinkle some porridge oats on the top of each muffin
Bake for 25-30 minutes. Test by poking a skewer into one of the muffins, if it comes out clean they are ready!