Preheat the oven at 175ºC and prepare the loaf cake pan with parchment paper.
Sift together the all-purpose flour, baking powder and salt, and set it aside. Mix together the buttermilk and vanilla extract and set it aside.
240 g all-purpose flour, 2 teaspoon baking powder, 1 teaspoon salt, 160 g buttermilk, 2 teaspoon vanilla extract
In a mixing bowl, using the paddle attachment add the butter and vegetable oil and granulated sugar and mix it on high speed for 2 min.
120 g butter, 45 g vegetable oil, 220 g granulated sugar
Add the eggs one at a time into the mixture and mix it in until combined.
3 large eggs
Continue by alternating between adding ⅓ of the flour mixture and ½ of the milk mixture, ending on the flour mixture. Mixing in each addition until just combined.
Add half of the dough to another bowl. To the other half add the Nutella and gently mix it in until combined.
100 g Nutella
Add the batter to the loaf pan by alternating between adding a scoop of the vanilla and the Nutella batter. With a knife swirl the two batters together. Bake it for 60-70 min or until a cake tester comes out clean.
Remove from the oven and let it cool down for 10 min. Then lift the loaf cake out of the pan and on to a cooling rack. Let the cake cool down completely on the cooling rack.