Prep the pan and oven. Heat your oven to 350°F (175°C). Line an 8-inch square pan with parchment, leaving a little overhang for easy lifting. Lightly grease the sides.

Warm the Nutella slightly. If your Nutella is stiff, microwave it for 15–20 seconds to loosen. This makes mixing easier and gives a smoother batter.

Whisk the wet ingredients. In a bowl, whisk the eggs until slightly frothy. Add Nutella and vanilla. Mix until glossy and well combined.

Add the dry ingredients. Sift in the flour, salt, and cocoa powder if using. Gently fold with a spatula just until there are no streaks. If the batter feels very thick, stir in the milk or espresso.

Fold in extras. Add chocolate chips or any mix-ins. Don’t overmix; you want to keep the batter thick for fudgy brownies.

Spread and smooth. Pour into the prepared pan and smooth the top with a spatula. For a Nutella swirl, dot a few teaspoons of Nutella on top and drag a knife through to create ribbons.

Bake. Bake for 18–24 minutes. They’re done when the edges look set and a toothpick inserted 2 inches from the edge comes out with a few moist crumbs. The center should look slightly soft but not jiggly.

Cool and slice. Let the brownies cool in the pan for at least 20–30 minutes. Lift out using the parchment and slice with a sharp knife, wiping the blade between cuts.