Preheat your oven to 325°F. Grease and line an 8-inch or 9-inch square baking pan with nonstick aluminum foil, parchment paper and set it aside. If you want to use regular aluminum foil, just grease it well with cooking oil spray.
In a large, heat-safe bowl, place the Nutella and warm it in the microwave or over a simmering pot of water just until it thins out a bit. This will make it easier to beat.
Add the eggs to the Nutella, and using a handheld mixer, beat until smooth and fluffy. Pump the handheld mixer up and down a few times to add more air into the batter.
Add the almond flour and beat again until well-combined. The mixture will be very thickly pourable and very sticky.
Transfer the brownie batter to the prepared baking pan and, using a small offset spatula, spread into an even layer. Smack the bottom of the pan a few times on the counter to break any large air bubbles.
Place the baking pan in the center of the preheated oven and bake for about 35 minutes for an 8-inch pan or about 30 minutes for a 9-inch pan. The brownies are done when the center of the pan of brownies is firm to the touch.
Remove from the oven and allow to cool to room temperature in the pan.
To make the brownies easier to slice, chill in the refrigerator for about 20 minutes. Remove the brownies from the pan and use a sharp knife to slice into 9 equal squares.
Store any leftover brownies in a sealed container in the refrigerator or freezer.