Bring a large pot of lightly salted water to a boil over high heat. Add the farfalle pasta, and cook until al dente, 8 to 10 minutes; drain.
Meanwhile, heat the olive oil in a large skillet over medium-high heat. Stir in the Italian sausage until crumbly and no longer pink, about 5 minutes. Stir in the garlic, and continue cooking until the sausage begins to brown, about 5 minutes more. Pour off the excess grease, then pour in the chicken stock and red pepper flakes. Bring to a boil over high heat, then add the broccoli rabe, and cover. Cook until the broccoli rabe is tender, about 4 minutes.
Stir in the butter, Parmesan cheese, salt, and pepper until the meat sauce has thickened. Toss with the farfalle and serve.