Cook the pasta: Bring a large pot of salted water to a boil. Add the pasta and cook according to the package instructions until al dente. Reserve 1 cup of pasta water, then drain and set aside.
- Sauté the vegetables: In a large skillet, heat olive oil over medium heat. Add diced onion and cook for 3-4 minutes until softened. Add minced garlic and cook for another 30 seconds until fragrant.
- Cook the mushrooms: Add sliced mushrooms and cook for 5-7 minutes, stirring occasionally, until the mushrooms release their moisture and turn golden brown.
- Add the spinach: Stir in chopped spinach and cook for another 2 minutes until wilted.
- Make the sauce: Pour in heavy cream and bring to a simmer. Let it cook for 3-4 minutes, allowing the sauce to thicken slightly.
- Combine pasta and sauce: Add cooked pasta to the skillet and toss gently to coat in the creamy sauce. If the sauce is too thick, add a bit of reserved pasta water to reach the desired consistency.
- Add the Parmesan: Stir in grated Parmesan cheese, continuing to toss until the cheese melts into the sauce. Season with salt and pepper to taste.
- Serve: Garnish with freshly chopped parsley and an extra sprinkle of Parmesan. Serve immediately.