Step 1: Preheat and Prep
Preheat your oven to 350°F (175°C). Line an 8×8 inch baking pan with parchment paper, leaving some overhang on the sides (this creates handles for easy removal later). Alternatively, grease the pan well and dust lightly with cocoa powder. Set aside.

Step 2: Mix Nutella and Eggs
In a large mixing bowl, combine the Nutella and eggs. If your Nutella is stiff from being cold, microwave it for 15-20 seconds to soften. Using a whisk or wooden spoon, beat the mixture vigorously until smooth and well combined. The mixture should look glossy and slightly lighter in color. This takes about 1-2 minutes of stirring. The eggs will help loosen the Nutella into a smooth batter.

Step 3: Add Sugar and Butter
Add the granulated sugar, melted butter (make sure it’s not hot, just melted), and vanilla extract to the Nutella mixture. Stir until completely smooth and well incorporated. The batter should be glossy and thick but pourable.

Step 4: Add Dry Ingredients
In a separate small bowl (or you can sift directly into the wet ingredients), whisk together the flour, cocoa powder, and salt to remove any lumps. Add the dry ingredients to the wet mixture. Using a rubber spatula or wooden spoon, gently fold the dry ingredients into the wet ingredients just until no flour streaks remain. Don’t overmix – stop as soon as everything is combined. Overmixing develops gluten and makes brownies cakey instead of fudgy.

Step 5: Add Mix-Ins (Optional)
If using chocolate chips or chopped hazelnuts, fold them in now, reserving a few to sprinkle on top if desired.

Step 6: Pour and Spread
Pour the brownie batter into your prepared pan. Use a rubber spatula to spread it evenly into all corners. The batter will be thick. Tap the pan gently on the counter a few times to release any air bubbles. If desired, add a few dollops of extra Nutella on top and swirl with a knife for a marbled effect, or sprinkle reserved chocolate chips and hazelnuts on top.

Step 7: Bake
Place the pan in the preheated oven and bake for 25-30 minutes. Start checking at 25 minutes. The brownies are done when the edges are set and pulling away slightly from the sides, the top has a shiny, crackly surface, and a toothpick inserted into the center comes out with a few moist crumbs (not wet batter, but not completely clean either). For ultra-fudgy brownies, err on the side of slightly underbaking. Remember, they continue cooking from residual heat after you remove them from the oven.

Step 8: Cool Completely
This is crucial! Remove the pan from the oven and place on a wire cooling rack. Let the brownies cool in the pan for at least 30 minutes, then use the parchment paper handles to lift the entire brownie slab out onto the cooling rack. Let cool completely (at least another 30 minutes to 1 hour) before cutting. Warm brownies are too soft to cut cleanly – patience results in perfect squares!

Step 9: Cut and Serve
Once completely cool, use a sharp knife to cut into 16 squares. For the cleanest cuts, wipe the knife with a damp cloth between each slice. Sprinkle with sea salt flakes if desired and serve. These are rich, so small squares are perfect!