3 pounds thin asparagus, trimmed and cut on the diagonal into 1 1/2 -inch
1 1/2 pounds leeks, white and tender green, halved lengthwise and sliced
crosswise 1 1/2 inches thick
12 scallions, cut into 1 1/2 -inch lengths
1/3 cup extra-virgin olive oil
3 tablespoons fresh lemon juice
Salt and freshly ground pepper
2 cups heavy cream
1/4 cup chopped dill
2 pounds dried fettuccine
3/4 pound smoked ham, cut into 2-by-1/4-inch strips
Freshly grated Parmesan cheese
Preheat the oven to 450°. In a large roasting pan, combine the asparagus, leeks, scallions, olive oil and half of the lemon juice; season with salt and pepper. Roast the vegetables, tossing once or twice, for 20 minutes, or until tender.
In a small saucepan, combine the cream and dill; season with salt and pepper. Bring to a boil, then remove from the heat, cover and keep warm.
Cook the pasta in a stockpot of boiling salted water until al dente. Drain well, reserving 1 cup of the cooking water. Return the pasta to the pot. Add the vegetables, ham, cream and the remaining 1 1/2 tablespoons of lemon juice and toss over low heat; add some of the cooking water if the pasta seems dry. Season with salt and pepper, transfer to a platter and serve. Pass the Parmesan separately.