INGREDIENTS
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1 stick (4 ounces) unsalted butter
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1/4 cup plus 2 tablespoons all-purpose flour
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1 quart whole milk
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1/2 cup homemade or store-bought tomato sauce
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Pinch of freshly grated nutmeg
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Salt and freshly ground pepper
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10 ounces white mushrooms, stems discarded and caps coarsely chopped
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1 medium onion, finely chopped
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1/4 pound thickly sliced prosciutto, finely chopped
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1 pound rigatoni
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1/2 pound imported Fontina cheese, coarsely shredded