Cook the pasta to al dente according to package instructions in salted water. Drain and set aside, reserving 1 cup of the pasta water.
Meanwhile in a large skillet on a medium-high heat, cook the pancetta or bacon until the fat renders
Add the red onion and sauté until soft over a medium-low heat - around 5-10 minutes.
Add the sliced mushrooms and cook until their color deepens- around 5 minutes.
Stir in the garlic. then add the white wine and let it bubble for a minute or two.
Add the stock then allow the sauce to simmer for 5 minutes to let the flavors come together.
Finish the sauce by adding the cream and Parmesan and gently stirring well. If the sauce needs it add a splash or two of the reserved pasta water so that the pasta is nicely coated in sauce.
Toss through the pasta and stir gently to reheat. Season again with salt and black pepper.
Serve with more freshly grated Parmesan and chopped parsley if you like.
