Preheat oven to 325°F (163°C). Lightly grease and flour a 9-by-5 inch loaf pan, tapping out any excess flour. Set aside.
In a medium size bowl, whisk together the eggs and vanilla extract until combined. Set aside. In another medium size bowl, combine the flour, baking powder, cinnamon, and salt together. Set that aside as well.
In the bowl of a stand mixer, or using a handheld mixer, beat the softened butter and sugar together on medium speed until light and fluffy; about 3 minutes. With the mixer running on low speed, add the egg/vanilla mixture and continue to beat until smooth and light in color. With the mixer running on low speed, slowly add the dry ingredients until just combined. The batter is very thick and very sticky. Do not overmix the batter.
Spread 1/3 of the batter into prepared loaf pan. Spread half of the Nutella on top. Nutella is very thick and hard to spread, but do your best to make it one even layer. It's easier if you warm if up just a bit. Repeat with another 1/3 of the batter and the rest of the Nutella. Top with remaining cake batter.
Bake the pound cake for 55-65 minutes. Cover with aluminum foil after 35 minutes to avoid the top and sides form browning too much. Slight browning is OK. The cake is done when a toothpick inserted in the center comes out free of cake crumbs (with some Nutella). The original recipe stated 1 hour and 15 minutes, but that was much too long for my cake. I fear it would be burnt and dry. 65 minutes is how long mine took, but yours may take longer.
Allow the cake to cool in the pan for 15 minutes on a wire rack. Invert the cake and let it come out of the pan. Turn it right side up and let it cool completely, about 2 hours, before slicing and serving. Cake stays soft, moist, and fresh stored at room temperature for up to 6 days.