Preheat the oven to 350 degrees F. Line a 9-by-13-inch baking pan with foil, leaving a 2-inch overhang on at least 2 sides. Butter the foil (not including the overhang).
Whisk together the flour, cocoa powder and salt in a medium bowl. Melt the butter and chocolate-hazelnut spread in a medium saucepan over medium heat, stirring frequently. Let cool slightly. Stir in the sugar and eggs. Add the flour mixture, and stir to combine. Pour the batter into the prepared pan, and bake until a toothpick comes out with just a few crumbs, 30 to 35 minutes.
Let the brownies cool completely in the pan on a cooling rack. Use the foil overhang to help lift them out of the pan. Cut into 16 squares. Store in an airtight container at room temperature for up to 3 days.
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