Bring a large pot of salted water to a boil over high heat. Add pasta and cook according to package directions or desired doneness. {Mine took about 12 minutes.} When the pasta is cooked, scoop it out with a slotted spoon into a bowl while you cook the broccoli rabe.
Bring the pasta water back up to a rolling boil add the broccoli rabe. Cook for about 1-2 minutes until the leaves have wilted down. Drain, saving about 2-3 tablespoons of the pasta water, and set aside.
Heat a tablespoon of olive oil in a large pan over medium-high heat. Add sausage (removed from casings); break up with a wooden spoon. Cook for 4-5 minutes or until no longer pink. Add minced garlic; cook for 1 minute. Add blanched broccoli rabe to the pan and salute for another 2-3 minutes or until heated through.
Add the cooked pasta to the pan, along with the butter. Toss everything to combine. Add cheese and a few tablespoons of pasta water and mix until the cheese is melted and the pasta is coated.
Before serving, squeeze some fresh lemon juice over top of the pasta and sprinkle with red pepper flakes and extra cheese if desired. Serve hot.