1. Fill a pot for the pasta with about 6 quarts of water, place over high heat, and bring to a boil.

2. Fill a 10-inch skillet (or asparagus cooker) with water, place over high heat, and bring to a boil.

3. Cut off the white, woody bottom part of the asparagus spears, then peel the remaining bottom third. Add 1 teaspoon salt to the boiling water, then gently slide in the asparagus. Cook until the asparagus is tender, 5 to 6 minutes, then lift it out and set aside. Save ½ cup of the water the asparagus cooked in.

4. While the asparagus is cooking, peel and finely chop the onion. Put the butter in a 12-inch skillet, add the chopped onion, and place over medium-high heat. Sauté until the onion has turned a rich golden color, about 5 minutes.

5. Cut the prosciutto slices into strips about 1/8 inch wide and 1 inch long. When the onion is ready, add the prosciutto and saute until it loses its raw color, 1 to 2 minutes.

6. Cut the asparagus into 1-inch lengths and add them to the pan. Continue sautéing until the asparagus becomes lightly colored, 2 to 3 minutes. Add the saved asparagus water and continue cooking until the liquid has evaporated completely, loosening any browned bits on the bottom of the skillet.

7. Add about 2 tablespoons salt to the boiling pasta water, add the penne, and stir well. Cook until al dente.

8. While the pasta is cooking, add the cream to the asparagus and cook until the cream has thickened, 1 to 2 minutes. Remove the pan from the heat.

9. When the pasta is done, drain well, toss with the sauce and the freshly grated Parmigiano-Reggiano, and serve at once.