Preheat oven to 325F. Grease and flour a loaf pan (approx 9*5)
Sift flour, baking powder and salt in a bowl and set aside
Whip the butter and sugar till nice and fluffy, 3 minutes.
Add the eggs one by one, beating for 45 seconds between each addition and scraping the sides
Mix in the Vanilla Extract
Now add in the flour in 3 increments, mixing until just combined
Put ⅓ of the batter in the prepared pan, add a few dollops of Nutella, follow by another third, more Nutella and then finally the remaining batter.
Run a butter knife or skewer through the batter to create swirls and bake for 1 hour and 10 minutes, check for doneness at the one hour mark by inserting a skewer/toothpick in the middle. Chocolatey bits of Nutella are fine, but the skewer should be clean otherwise
Video
Notes
Changing the pan size will change bake times. Roughly speaking if you use a larger pan then you need to reduce time. If you have an oven light then turn it on before opening the oven door to check for doneness. If you open too early the cake will deflate/not rise properly.