Bring a large pot of water to a boil, salt it, add the pasta and cook until al dente. Drain.
While the pasta is working, in a large skillet, heat the EVOO, two turns of the pan, over medium-high heat. Add the pancetta, if using, and cook until the fat renders, about 2 minutes. Stir in the cauliflower, onion, garlic and rosemary; season with salt, pepper and a little nutmeg. Cook, stirring occasionally, until just softened, about 2 minutes. Add the wine and cook until slightly reduced, about 1 minute. Add the stock and cook until reduced by half, about 5 minutes.
Add the pasta and cheese and toss. Serve in shallow bowls, topped with the watercress.