Directions

1. In a large pot of boiling salted water, cook pasta until al dente, according to package instructions. Reserve 1/2 cup pasta water; drain pasta, and return to pot.
2. While pasta is cooking, heat 1 tablespoon butter in a large skillet over medium. Add leeks; season with salt and pepper. Cook, stirring occasionally, until tender, 3 to 5 minutes. Add peas; cook, stirring, until warmed through, 2 to 3 minutes.
3. To drained pasta, add leek mixture, remaining 3 tablespoons butter, lemon juice, and prosciutto; season with salt and pepper. Add reserved pasta water a little at a time, tossing, until a thin sauce coats pasta. (You may not need all the water.) Serve, sprinkled with ricotta salata.