First make the sauce. In a skillet heat oil. Add shallots and cook, stirring for 1 minute. Then add mushrooms and cook, stirring occasionally for 5 minutes, or until mushrooms are lightly golden. Now stir in garlic, prosciutto, and red pepper flakes and cook for 30 minutes, and then add chicken stock or broth and simmer for 1 minute. To your pasta, bring a large pot of water to a full rolling boil. When the water is ready, add your pasta. Remember start your cooking time when the water returns to a boil, not when you add the pasta. Cook your pasta according to package directions, after 6 minutes of cooking, add the broccoli rabe to the cooking pasta. Drain pasta and broccoli rabe in a colander and transfer to a serving dish. Top with sauce, mixing well. Garnish if desired.