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In a covered pasta pot over high heat, bring water to a rapid boil.
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Meanwhile, in a large saute pan, heat olive oil over medium heat.
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Add 1/2 cup of the walnuts and the cinnamon and cook, stirring, until walnuts begin to brown, about 5 minutes.
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Add cream, season to taste with salt and pepper and stir once (sauce will be very thick).
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Cover and remove pan from heat and set aside.
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Add salt and spaghetti to the boiling water and cook, uncovered, until pasta is al dente.
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Scoop out about 1 cup of the pasta water and set aside; drain pasta.
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Add 1/4 cup of the reserved pasta water to the walnut mixture and increase heat to high.
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Add in spaghetti and , using pasta tongs, toss to coat evenly, adding more pasta water if needed.
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Add half of the Parmigiano-Reggiano and toss well.
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Transfer to a large serving platter and sprinkle with remaining cheese and walnuts.
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Serve immediately.