INGREDIENTS
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1 pound spaghetti
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1 cup chicken stock
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6 tablespoons unsalted butter, divided
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2 tablespoons chopped fresh rosemary, plus 4 to 6 sprigs for garnish
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1/2 cup finely chopped onions
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1/4 cup grated Parmesan cheese, plus more for the table
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6 cloves garlic, chopped coarsely
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Kosher or sea salt and black pepper to taste