Place a large saute pan over medium-high heat. When the pan is hot, add a film of oil along with the onions and a pinch of salt. Cook, stirring occasionally, until the onions begin to soften and caramelize, 2 to 3 minutes. Move the onions to one side of the pan, and then add the butter, cabbage and a pinch of salt. Cook until everything is caramelized and softened, 4 to 5 minutes. Add the chicken stock. Simmer this mixture until the cabbage is cooked through and the liquid has reduced, about 5 minutes.
In the meantime, drop your pasta. Cook at a gentle boil for 2 minutes less than the package directions. Then drain and add to the cabbage mixture. Gently fold in the parsley and sour cream and serve immediately, adding black pepper and a drizzle of oil.