Step 1

In a 12-inch skillet over medium, melt the butter. Add the shallots and cook, stirring occasionally, until softened and translucent, 3 to 5 minutes. Stir in the cream, lemon zest, half of the Parmesan and ½ teaspoon pepper; remove from the heat and set aside.

Step 2

In a large pot, bring 2 quarts water to a boil. Add the pasta, asparagus and 2 teaspoons salt; cook, stirring occasionally, until the pasta is al dente and the asparagus is tender-crisp. Reserve about 1 cup of the cooking water, then briefly drain in a colander, leaving water clinging to the pasta.

Step 3

Immediately add the pasta mixture and ½ cup of the reserved pasta water to the skillet. Cook over medium heat, tossing with tongs, until the pasta is lightly sauced, 1 to 2 minutes; add more reserved pasta water as needed so the sauce clings to the noodles. Add the lemon juice, then taste and season with salt and pepper. Transfer to a serving platter or individual bowls, then scatter on the prosciutto and sprinkle with the remaining Parmesan.