INGREDIENTS
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1/4 cup olive oil
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1 small yellow onion, finely chopped
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2 teaspoons coarse salt
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2 pounds baby spinach
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4 tablespoons unsalted butter
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1/4 cup all purpose flour
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1 quart milk
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1 packed cup grated Parmesan (3 ounces)
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1/4 teaspoon freshly grated nutmeg
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1/4 teaspoon ground black pepper
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2 medium zucchini (about 1 pound), sliced lengthwise into 1/4-inch-thick planks
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8 ounces no-boil lasagna noodles
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6 ounces mozzarella, shredded
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1/3 packed cup (1 ounce) grated Pecorino Romano