Preheat the oven to 180 degrees Celcius. In a large bowl fitted to a stand mixer, using the paddle attachment, beat 1 ½ cups Nutella and 4 eggs until the mixture is about doubled in volume, 2-3 minutes.
Add the flour to the Nutella mixture and using a spatula, gently fold until just incorporated.
Transfer the batter to a greased 8-inch cake pan lined with Twinsaver baking paper.
Transfer the prepared cake to the middle rack of the oven and bake, rotating halfway through, until the cake is puffy in the middle and a toothpick inserted comes out clean, about 40 minutes.
Remove the cake from the oven and set aside to cool in the pan for about 15 minutes, then unmold and cool completely on a wire rack.
Frost the top of the cooled cake with the remaining ½ cup of Nutella. Slice it up, share, and enjoy.