Step 1

In a food processor, pulse the the asparagus until finely chopped, about 15 pulses. Measure out 1½ cups chopped asparagus and set aside.

Step 2

In a large pot, bring 4 quarts water to a boil. Add 2 tablespoons salt and the pasta, then cook, stirring occasionally, until the pasta is al dente. Reserve 1 cup of the cooking water, then drain.

Step 3

Meanwhile, in a nonstick 12-inch skillet over medium-high, melt the butter. Add the garlic, shallots and ½ teaspoon salt, then cook, stirring occasionally, until the shallots are softened, 1 to 2 minutes. Add the asparagus in the processor and cook, stirring often, for 2 minutes. Add the cream and the reserved 1½ cups asparagus, then bring to a simmer over medium. Cook, stirring often, until a spoon drawn through the mixture leaves a 2-second trail, 2 to 3 minutes. Remove from the heat and stir in the Parmesan and ¼ teaspoon salt.

Step 4

Add the drained pasta and ¼ cup of the reserved cooking water to the asparagus-cream mixture and set the pan over medium. Toss, adding cooking water 1 tablespoon at a time as needed, until the sauce is silky and clings to the pasta. Stir in the lemon zest, then taste and season with salt and pepper. Serve with additional Parmesan and lemon wedges.