Combine the milk and vinegar in a small bowl and set aside for 10 minutes.
Preheat the oven to 180°C and line a muffin pan with baking paper cases.
Whisk together the self-raising flour, cinnamon and salt in a medium bowl.
In a large bowl, beat the butter and brown sugar until smooth and creamy.
Add the eggs one at a time, beating well after each addition.
Add the milk mixture, vanilla and mashed banana. Mix until well combined.
Fold in the dry ingredients until just combined, taking care not to overmix.
Divide the batter evenly between the muffin cases, filling each about three-quarters full.
Bake for 18–22 minutes, until the muffins are golden and a skewer inserted into the centre comes out clean.
Transfer to a wire rack and leave to cool completely.
Beat the cream cheese and butter together until smooth.
Add the icing sugar, cinnamon, vanilla and salt. Beat until light and fluffy.
Pipe or spread the frosting over the cooled muffins and finish with a light dusting of cinnamon.