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Preheat the oven to 350 degrees.  Spray an 8-inch square baking dish with cooking spray and set aside.
														 
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Combine the chocolate and butter in medium a microwave-safe bowl and heat in 30-second intervals, stirring after each interval, until chocolate is melted and mixture is smooth.
														 
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Set aside to cool for 5 minutes.
														 
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Stir the eggs and sugar into the chocolate mixture, mixing well.  Mix in the vanilla, baking soda, and salt until well combined.
														 
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Fold in the flour, until just combined (just mix until you no longer see streaks of flour in the brownie batter).
														 
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Fold in the hazelnuts.
														 
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Pour the batter into the prepared pan and smooth the top.  Dollop the Nutella over the brownie batter and use a butter knife to swirl the two together.
														 
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Bake for 25 to 30 minutes, until the top of the brownies looks set.  Set pan on a wire rack and cool completely before slicing and serving.