Preheat the oven to 180°C and place 12 muffin liners into a muffin tin.
In a mixer with a paddle attachment attached, place the flour, sugar, baking powder, eggs, oil, milk and vanilla essence and mix until combined.
Fold the mashed banana into the mixture.
Add a tablespoon of the mixture to each muffin case and then place 1/2 a tablespoon of nutella in the centre on top of the mixture in the muffin case. Divide the remaining mixture between the 12 muffin cases on top of the nutella.
Place in the oven and bake for 20 - 25 minutes.
Remove from the oven, allow to cool for a couple of minutes before placing on a cooling rack to cool completely.