Meanwhile, in a large, heavy skillet, heat the oil over a medium flame. Add the sausage and cook, breaking up with a spoon, until the sausage is brown and juices form, about 8 minutes. Add the garlic and red pepper flakes, and sauté until fragrant, about 30 seconds. Remove the broccoli rabe from the cold water, add to the skillet and toss to coat. Add the pasta and enough reserved cooking liquid, about 1/4 cup and stir to moisten. Stir the Parmesan cheese, salt to taste, and pepper into the pasta mixture. Transfer to pasta bowls and serve. Enjoy!