Boil water for pasta; continue recipe while waiting. Cook pasta, drain when done. Toss with a bit of the olive oil.
Remove sausage casings. Heat a large skillet. Add remaining olive oil at medium heat. Add garlic, sauté a minute or two, then crumble sausage into oil. Move around till cooked, add butter and melt, then lower heat and simmer 20 minutes.
Wash broccoli rabe, and coarsely cut up; I generally cut each stem into 3 pieces. Put on top of sausage mixture and cover. Once it wilts a bit, stir it together. Cook until broccoli rabe is done to your liking.
Add sausage mixture to pasta and toss with 1/2 of the parmesan. Serve immediately with remaining parmesan on the side.