Chocolate Hazelnut Banana Bread
1 1/3 cups / 7 oz / 210 g all-purpose flour
1 tsp baking soda
2/3 tsp baking powder
1/2 tsp salt
1/2 cup / 3,3 oz/ 100 g unsalted butter, softened
2 tbsp / 1 oz / 35 ml vegetable oil
1/2 cup/ 3,3 oz/ 100 g light brown sugar
1/4 cup/ 1,5 oz/ 50 g white sugar
1 1/4 tsp vanilla extract 
2 eggs, room temperature
2 tbsp / 1 oz/ 30 g sour cream or natural yogurt
3 medium overripe bananas, peeled and chopped or minced with a fork 
3 tbsp / 1,5 oz/ 50 g nutella
3 tbsp/ 1 oz/ 25 g shelled hazelnuts, chopped
2 bananas, extra, for topping

Preheat the oven to 375°F/ 180°C. Line a 4,5x10" /13x25 cm loaf pan with baking paper.      

In a medium bowl, mix together the flour, baking soda and powder, and salt.      

In a bowl of a stand mixer, beat together the oil, butter, both sugars and vanilla extract on high until light and pale. Add in the eggs, one at a time, continuing to beat until fully incorporated before adding the next egg in. Add the sour cream, bananas and beat until combined.     

Using a spatula, gradually mix in the flour mixture to the batter until just combined. Do not overmix.      

Transfer the batter to the prepared loaf pan, smoothen the surface with the spatula. Spoon the nutella randomly over the batter. Using a skewer, draw random lines and/or loops, creating a marble effect. Sprinkle with half of the hazelnuts. Skin and slice the 2 extra bananas lengthways and place them atop of the cake. Sprinkle the remaining hazelnuts over.       
Bake in the preheated oven for 30-40 minutes or until golden brown and baked through. Test the doneness with a wooden skewer: poke the cake in the centre, the cake is done if the skewer comes out clean. Remove the pan from the oven, rest for 10 minutes, then transfer the cake to a wire rack top side up to cool completely.