Broccoli Rabe, Spicy Italian Sausage and Beans over Pasta

"To prepare broccoli rabe for cooking, cut leafy portions into 2 inch pieces. Peel the stem and cut to 2 inch pieces.In large deep skillet saute onion in oil for 5 or 6 minutes until translucent, then add garlic and crushed red pepper (if using) for an additional 2 minutes.Push onion and garlic to side of pan or set aside in small dish.Using same skillet, saute sausage , mashing with a fork, until lightly browned. Return onion and garlic to skillet, add broccoli rabe, and stock. Season with salt and pepper and cook, stirring occasionally for about 10 minutes until the broccoli rabe is tender. Add drained beans and stir until thoroughly mixed and heated.While sauce is cooking, bring a large pot of salted water to a boil.Cook pasta according to directions for desired doneness and when draining pasta, reserve 1-cup pasta cooking water. Plate pasta with sauce, using reserved water if more moisture is needed and top with grated cheese."