Bring a large pot of salted water to a boil and cook the fettuccine according to package directions until al dente. Drain and set aside.
While the pasta cooks, heat the butter and olive oil in a large skillet over medium heat. Add the sliced mushrooms and cook until they release their liquid and turn golden, about 6 minutes.
Stir in the minced garlic and cook for 1 minute until fragrant.
Add the fresh spinach and cook until it wilts, about 2 minutes.
Pour in the heavy cream and bring to a gentle simmer. Stir in the grated Parmesan cheese until it melts and the sauce thickens slightly.
Add the drained fettuccine to the skillet and toss until the pasta is evenly coated. Season with salt and black pepper to taste before serving.