Preheat your oven to 180C, grease your loaf pan with butter and line with parchment paper. Mash the bananas and set aside.
In a mixing bowl combine the sugar, butter, egg, milk and vanilla and mix until smooth.
In another bowl add all the dry ingredients and whisk.
Add the dry ingredients to the butter mixture and mix until just smooth.
Add the mashed bananas and mix until they are combined (don’t over mix).
Soften the Nutella in the microwave for 20 seconds, then add 2/3 of it to the cake batter and gently fold (doesn’t have to be completely folded you still can see swirls).
Pour into the prepared pan and drizzle the rest of the Nutella and make swirls with a knife.
Bake for about 45 minutes.
Cool in the pan for 10 minutes, then flip on a wire rack until completely cooled. Serve with extra Nutella.