Preheat your oven to 350°F. Prepare an 8-inch square baking pan by lining it with parchment paper, allowing some overhang for easy removal.

In a large bowl, beat the softened butter until smooth. Add brown sugar and continue beating until creamy.

Mix in the eggs and vanilla extract until well combined. Then, blend in 1 cup of the chocolate hazelnut spread and salt until the mixture is smooth.

Transfer the batter to the prepared pan. Drop small dollops of the remaining chocolate hazelnut spread over the top and use a knife to create a swirl pattern.

Bake for about 32-36 minutes. Check for doneness with a toothpick; it should come out with a few moist crumbs attached.

Let the brownies cool completely in the pan on a wire rack. Once cool, use the parchment paper overhang to lift them out and cut into squares.