- With the rack in the middle position, preheat the oven to 325°F (170°C). Line the bottom of an 8-inch (20 cm) square baking pan with parchment paper, letting the paper hang over two sides. Butter the two other sides.
- In a bowl, combine the flour and salt. Set aside.
- In another bowl, beat the eggs, hazelnut spread, brown sugar and vanilla extract with an electric mixer until smooth, about 2 minutes. With the mixer on low speed, add the flour mixture alternately with the melted butter.
- Spread the batter into the prepared pan. Bake for 35 to 40 minutes or until a toothpick inserted into the centre comes out with a few lumps and not completely clean.
- Let cool in the pan for about 2 hours. Unmould and cut into squares.
- Serve at room temperature.