Wash the mushrooms, slice into small pieces and saute them with sunflower oil in a hot pan. Season with rosemary and set aside.
Sweat the sliced onion in butter then add half of the cabbage leaves with the onions, season with salt and let them cook for 10 minutes. Add the vegetable stock and boil for another 15 minutes, then add the corn starch dissolved in cold water and let it cook for another 3 minutes. Add the chopped sage and season with chilli flakes.
Cook the pasta for 9 minutes in boiling salted water. Add the remaining sliced savoy cabbage after 7 minutes. Drain, add to the sauce and season well. Finish by adding the mushrooms and lemon zest then serve.
