Cook the tortellini according to package directions in salted water. Save ½ cup of pasta water.
In a large saucepan, add butter, chopped shallot and prosciutto over medium heat, cooking 3 minutes. Add the cream, salt and pepper and simmer for 1 minute.
Add ½ of the Parmesan to the sauce and mix until melted through. Add the cooked tortellini and peas to the sauce. Toss a couple of times and add the remaining Parmesan, tossing to combine. If sauce is dry, add pasta water 2 tablespoon at a time until it is smooth.
Sprinkle some chopped Italian parsley and more Parmesan on top. Serve immediately.
Notes
Make sure the water you are cooking the pasta in is salted as some of the flavor comes from it.
DO NOT overcook the tortellini when boiling. You want it just al dente or slightly under. It continues to cook with the sauce.
Use a high fat content cream as it thickens when it cooks so you don't need a roux.
Don't use pre-shredded cheese. You want if finely grated so it melts well. Pre-shredded has added ingredients that will just make it clump up.
If omitting the prosciutto, add additional salt to the dish.