Preheat oven to 425 F. Combine cauliflower florets, salt, 3 Tbsp olive oil, and 2 cloves chopped garlic in a bowl and toss. Put on a baking sheet and roast for 30 minutes. Stir together bread crumbs, salt, and 1 tablespoon oil in a small bowl until combined well. Transfer to a large skillet and cook over medium heat, stirring, until crisp and golden, 3 to 5 minutes, then return to bowl. When the cauliflower is out of the oven, heat the remaining oil in a skillet over moderately high heat until hot but not smoking. Then sauté the prosciutto and cauliflower, stirring occasionally, for about 3 minutes. Stir in the remaining garlic and red pepper flakes and saute for 1 minute. Add the broth, reduce to simmer, and partially cover the pan. Stir occasionally until the cauliflower is tender, about 6 minutes. While the sauce simmers, cook the pasta in a 6- to 8-quart pot of boiling salted water , uncovered, until al dente, then pour into a colander to drain. Stir the parmesan into the sauce and simmer 1 minute. Toss pasta with the cauliflower mixture and parsley in a large bowl, then sprinkle with the bread crumbs. Serve with additional cheese.