Preheat your oven to 325. Prepare a 9 inch square pan by lining it with parchment paper and spraying it with non stick spray.
In a small bowl, sift flour and salt together. Set aside.
In another bowl, mix Nutella, eggs, brown sugar and vanilla on low speed until well incorporated and creamy...about 2 minutes or so.
Add flour mixture in 2 batches, alternating with the melted butter. Spread in your pan and bake for 35-20 minutes. I started to check mine at about 25 minutes. You want the center to be just set, if you like them fudgey like I do.