Cook the pasta according to package directions.
Reserve 1/4 cup of the cooking liquid, drain the
pasta and return it to the pot.
Meanwhile, heat the oil in a large skillet over
medium-low heat. Add the leeks, onion and 1/4 tsp
each salt and pepper and cook, covered, stirring
occasionally, until very tender, 6 to 8 minutes.
Stir in the garlic and cook for 1 minute.
Whisk in the milk and bring to a simmer. Whisk in
the cream cheese, Parmesan and nutmeg. Stir in
the peas and simmer, stirring occasionally, until
slightly thickened, 2 to 3 minutes.
Toss the pasta with the cream sauce and ham,
adding some of the reserved cooking liquid if the
pasta seems dry.