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1
Fill a pot for the pasta with about 6 quarts of water, place over high heat, and bring to a boil.
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2
Put about 1 inch of water in a pot large enough to cook the spinach.
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3
Place it over high heat.
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4
When the water boils, add 1 teaspoon salt and the spinach.
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5
Cook until the spinach is quite tender, 5 to 6 minutes.
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6
Drain in a colander and squeeze out as much water as possible by pressing on the spinach with a spoon.
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7
Transfer the spinach to a cutting board and finely chop it.
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8
While the spinach is cooking, peel the onion and finely chop it.
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9
Put the butter in a 12-inch skillet, add the onion, and place over medium-high heat.
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10
Saute the onion until it turns a rich golden color, about 5 minutes.
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11
When the water for the pasta is boiling, add about 2 tablespoons salt, add the penne, and stir well.
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12
Cook until al dente.
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13
When the onion is ready, add the spinach and saute, stirring often, for about 5 minutes.
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14
Add the ricotta, cream, and nutmeg, and cook until the ricotta has heated through and the cream is reduced, 2 to 3 minutes.
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15
Taste and adjust for salt and season with pepper, then remove from the heat.
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16
When the pasta is done, drain well, toss with the sauce and the Parmigiano-Reggiano, and serve at once.
