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Preheat oven to 350°F.
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Sift together flour, cocoa, baking powder, baking soda and salt in a medium bowl.
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Beat eggs in a large bowl until frothy.
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Add sugar and continue beating on high for 2 minutes.
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Stir in Nutella.
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Add flour mixture to egg mixture and stir until well combined.
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Stir in chocolate chips and hazelnuts, if using.
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Divide dough into 2 or 3 logs with well floured hands and arrange on a parchment lined baking sheet. Press logs into rectangles approximately 1/2 inch thick.
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Bake at 350F for 20 minutes.
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Remove from oven.
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Turn down oven heat to 300°F.
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Using a serrated knife, cut logs into 1/3-1/2 inch slices. Arrange on baking sheet and return to oven.
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Bake for 10-12 minutes, turn biscotti over and bake an additional 10-12 minutes (depending on the thickness of your slices).
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Remove to a wire rack to cool. Store in an airtight container.