Cook the pasta according to the package directions.
Meanwhile, heat the oil in a large skillet over medium-high heat. Add the onion and ¼ teaspoon each salt and pepper.
Cook the onion, stirring occasionally, until softened, 4 to 6 minutes.
Add the cabbage and broth and cook, stirring occasionally, until the cabbage begins to wilt, 2 to 3 minutes.
Stir in the prosciutto, butter, and sage and cook until the butter has melted. Serve over the pasta.