Cook the pasta: Cook pasta in salted water according to package instructions until al dente. Reserve 1/2 cup pasta water, then drain.
Sauté the mushrooms: Heat olive oil in a large skillet over medium heat. Add mushrooms and cook 5–6 minutes until golden and tender.
Add garlic and spinach: Add garlic and cook 30 seconds until fragrant. Add spinach and cook until wilted.
Make the creamy sauce: Pour in heavy cream, season with salt, pepper, and nutmeg. Simmer gently 2–3 minutes.
Combine pasta and sauce: Add cooked pasta to the skillet. Toss to coat, adding reserved pasta water as needed. Stir in Parmesan until creamy.
Serve: Serve hot, garnished with extra Parmesan and fresh herbs.