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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
Fill a 10-inch skillet (or asparagus cooker) with water, place over high heat, and bring to a boil.
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3
Cut off the white, woody bottom part of the asparagus spears, then peel the remaining bottom third.
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4
Add 1 teaspoon salt to the boiling water, then gently slide in the asparagus.
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5
Cook until the asparagus is tender, 5 to 6 minutes, then lift it out and set aside.
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6
Save 1/2 cup of the water the asparagus cooked in.
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7
While the asparagus is cooking, peel and finely chop the onion.
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8
Put the butter in a 12-inch skillet, add the chopped onion, and place over medium-high heat.
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9
Saute until the onion has turned a rich golden color, about 5 minutes.
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10
Cut the prosciutto slices into strips about 1/8 inch wide and 1 inch long.
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11
When the onion is ready, add the prosciutto and saute until it loses its raw color, 1 to 2 minutes.
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12
Cut the asparagus into 1-inch lengths and add them to the pan.
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13
Continue sauteing until the asparagus becomes lightly colored, 2 to 3 minutes.
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14
Add the saved asparagus water and continue cooking until the liquid has evaporated completely, loosening any browned bits on the bottom of the skillet.
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15
Add about 2 tablespoons salt to the boiling pasta water, add the penne, and stir well.
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16
Cook until al dente.
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17
While the pasta is cooking, add the cream to the asparagus and cook until the cream has thickened, 1 to 2 minutes.
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18
Remove the pan from the heat.
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19
When the pasta is done, drain well, toss with the sauce and the freshly grated Parmigiano-Reggiano, and serve at once.
