Boil water in a large pot, seasoning generously with salt. Add pasta and cook for about 2 minutes (if using fresh pasta). You want the pasta to be about a minute from al dente (or fully al dente with thicker fresh pasta) so that it can finish cooking in the sauce. Reserve 1 cup of the pasta water and then drain.
In a large sauté pan, melt 4 tablespoons of butter. Add the shallots and sauté for 2 minutes. Add the prosciutto pieces and sauté until browned, about 3 minutes.
Sprinkle in the crushed red pepper flakes and sauté for 1 minute. Add heavy cream, orange juice, orange zest, and ½ cup reserved pasta water. Bring mixture to a boil and add the almost-cooked pasta, peas, and remaining ½ tablespoon butter. Once pasta is cooked, season with salt and pepper to taste.
