In a large pot, heat the oil over medium heat. Add the diced onions, sliced mushrooms, and salt and sauté until the mushrooms are soft and have cooked down.

Pour in the cream or half and half and black pepper. Let it simmer gently until the sauce starts to thicken.

Add the cooked hot pasta to the pot or pour the sauce over the pasta and mix well until everything is evenly coated.

Taste and adjust with more salt and pepper if needed.