Preheat oven to 325 degrees F.

Line 9x13" baking dish with foil, then spray with non-stick cooking spray.

In medium saucepan, melt butter over medium heat. Stirring constantly, cook until butter turns amber (about 5-7 minutes). Keep a close eye on it, as it will burn quickly.

In large bowl, combine brown butter, sugar, cocoa powder, vanilla, water, and salt. Let cool for about 5 minutes.

Add the eggs to the butter and sugar mixture, whisking constantly as you add them, and beat until mixture is smooth.

Stir in flour.

Pour in prepared pan.

Spoon Nutella into a plastic baggie, then microwave for 20 seconds. Snip the corner off one side of the baggie, then squeeze out into rows the short way of the baking dish.

Then, using a knife, run perpendicular to the rows, making a swirl.

Bake in preheated oven for 30 minutes, or until toothpick inserted in the center comes out with a few crumbs attached.

Sprinkle with sea salt.

Cool in pan, then cut into squares and enjoy!