Place a rack in the center of the oven and preheat the oven to 325 degrees F. Butter a 9 x 5 loaf pan, dust the insides with flour and tap out the excess. Set aside for later use.

In a medium sized bowl, beat the eggs and the vanilla until just combined, set aside for later use. In another medium size bowl, combine the flour, baking powder, cinnamon, and salt together. Set that aside as well.

With a hand or stand mixer, fitted with the paddle attachment, cream the butter and sugar together, about 3 minutes. Set the speed to low and add in the egg/vanilla mixture. Continue to mix until everything is well incorporated then add the milk. With the mixer running on low speed, slowly add the dry ingredients until just combined. The batter is quite thick and very sticky. Do not overmix the batter.

Spread half of the batter in the prepared pan, then spread half of the Nutella on top. Repeat with rest of the batter and the remaining Nutella. Lightly swirl the Nutella into the batter with a butter knife. Do not overmix.

Bake the cake for about 65 - 75 minutes. Cover with an aluminum foil after 35 minutes of baking so the top layer does not become burnt. The cake is done when a toothpick inserted in the center comes out clean ( a few crumbs or a smear of nutella is okay).

Let the cake cool in the pan for 15 minutes before inverting the cake onto a wire rack. Cake will stay fresh for up to 5 days at room temperature in an air tight container.