Preheat the oven to gas mark 4/350oF/180oC/160oC fan and line a 12-count muffin tin with 12 muffin cases.
In a blender, combine the milk and ripened bananas until smooth and set aside. If you're not using a blender then mash the bananas with a fork and set aside. If the bananas are well ripened, they may start to turn browner as you mash them but they are still ideal to use.
In a mixing bowl, cream together the vegetable fat spread and caster sugar until smooth. Add the vegetable oil and the eggs and combine all the ingredients together. Pour in the banana and milk mixture. If you used a fork to mash the bananas then pour in the milk and then add the mashed bananas. Add the vanilla extract and cinnamon and continue to mix.
Sift and pour in the self-raising flour and continue to mix until well combined. Stop mixing as soon as the ingredients are all incorporated. Spoon the mixture carefully into the muffin cases and ensure each case is around two-thirds full. Bake for 20 minutes or until a cake tester comes out clean.
Allow the muffins to cool for 10 minutes then transfer to a cooling rack to completely cool. Once they are completely cooled, dust with icing sugar and enjoy.