Preheat the oven to 325°F. Spray an 8x8 inch pan with nonstick spray, then line it with parchment paper, allowing the paper to extend over two opposite sides.
In a small bowl, combine the flour and salt.
In a large bowl, use an electric mixer to combine the Nutella, brown sugar, eggs and vanilla. Beat until smooth. With the mixer running on low, add the flour mixture in two parts, alternating with the melted butter.
Scrape the batter into the prepared pan. Bake 30 to 35 minutes, or until a toothpick inserted into the center comes out fairly clean. I found them to be just right at about 32 minutes.
Cool in the pan for a couple of hours. Cut into squares and serve. Store in a covered container.