How to Make It
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.