Bring a large pot of lightly salted water to a boil over high heat. Add the pasta and cook until al dente, 8 to 10 minutes; drain.
Meanwhile, heat the olive oil in a large frypan over medium-high heat. Stir in the Italian sausages and break up until crumbly and no longer pink, about 5 minutes. Stir in the garlic and continue cooking until the sausages begin to brown, about 5 minutes more.
Pour off the excess grease then pour in the chicken stock and chilli 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.
When the broccoli rabe is done, stir in the butter, Parmesan cheese, salt and pepper until the meat sauce has thickened. Toss with the farfalle and serve.