Heat 1/4 cup olive oil in a large skillet over medium heat.

Add chopped onion, celery, and rosemary to the skillet.

Sauté the vegetables until they are tender, about 10 minutes.

Add butternut squash, plum tomatoes, and 1/2 cup water to the skillet.

Bring the mixture to a boil.

Reduce heat to medium-low, cover the skillet, and simmer until the squash is tender, about 20 minutes.

Stir in finely chopped prosciutto and fresh parsley.

Cook pasta in a large pot of boiling salted water until al dente (tender but firm to the bite).

Drain the pasta and return it to the pot.

Add 2 tablespoons of olive oil, the squash mixture, and 1/2 cup of grated Parmesan cheese to the pasta.

Toss the pasta to combine.

Season with salt and pepper to taste.

Transfer the pasta to a serving bowl.

Sprinkle with the remaining 1/4 cup of Parmesan cheese.