Preheat the oven to 325˚F. Line an 8x8 baking pan with parchment paper.
In a medium bowl, mix together the flour and salt. Set aside.
In a separate bowl, beat together the Nutella, brown sugar, vanilla and eggs until smooth.
Alternate between adding the flour and the butter into the Nutella mixture, and blend until fully combined.
Pour batter into the prepared pan, and bake for 50-55 minutes, or until a toothpick inserted comes out with only a couple of crumbs.
Remove from oven, and let cool for about an hour.