Preheat the oven to 325 . Lightly grease and flour a 9x5 inch loaf pan, tap out excess flour. In a medium bowl, whisk the 1-1/2 cups of flour with the baking powder and salt and set aside.
In a large bowl beat the butter with the sugar at medium-high speed until fluffy, about 3 minutes. With the mixer at medium-low speed, add the eggs, one at a time, making sure each one gets incorporated before adding the next one. Add the vanilla . Add the flour mixture in 3 batches, beating at low speed between additions until incorporated. Continue to beat for 30 seconds longer.
Spread one-third of the batter in the prepared pan, then spread half of the Nutella on top. Repeat with another third of the batter and the remaining Nutella. Top with the remaining batter. Lightly swirl the Nutella into the batter with a butter knife. Don't overmix.
Bake for about 1 hour and 10 minutes, until a toothpick inserted in the center comes out clean. Let the cake cool in the pan for 15 minutes. Invert the cake onto a wire rack, turn it right side up and let cool completely, about 2 hours.