How to Make It
In a large pot of salted boiling water, blanch the cabbage until just tender, 4 to 5 minutes. Using a slotted spoon, transfer the cabbage to a colander. Cool the cabbage under running water and drain well.
In a large skillet, heat the oil until shimmering. Add the onion and a generous pinch of salt; cook over moderate heat, stirring, until softened, 7 minutes. Add the sausage and cook, stirring, until no pink remains, 7 minutes. Stir in the tomato sauce and cabbage. Cover and simmer over moderately low heat, stirring, until the cabbage is tender, 15 minutes.
Return the cabbage cooking water to a boil. Add the fettuccine and cook until just barely al dente. Drain the pasta, reserving 1/4 cup of the cooking water. Add the pasta and reserved cooking water to the cabbage sauce. Cook over moderate heat, tossing, until the pasta is coated and al dente, about 2 minutes. Transfer the pasta to shallow bowls, sprinkle cheese on top and serve.