Preheat broiler. Bring a large pot of salted water to a boil. IN medium skillet, heat 1 T. of the olive oil. Add the garlic and cook over medium heat until lightly golden, about 3 minutes. Add cream and simmer until thickened slightly, about 2 minutes. Season the garlic cream with salt and pepper. Cook rigatoni until al dente; about 6 minutes before the rigatoni is done, add cauliflower florets to pot. Drain, reserving 2 T. of the pasta cooking water. Meanwhile, in medium bowl, toss panko with Parmigiano and remaining 2 1/2 T. olive oil; season with salt and pepper. Return rigatoni and cauliflower to pot. Add garlic cream, the prosciutto and the reserved pasta water and toss until pasta is coated. Scrape pasta into large shallow baking dish and sprinkle the panko mixture evenly over the top. Broil for about 2 minutes, rotating constantly until topping is evenly browned. Serve hot.