1. Bring a large pot of salted water to a boil. Add the fettuccine and cook according to package instructions until al dente. Drain and set aside.
2. In a large skillet, heat the olive oil over medium heat. Add the onion and sauté until translucent, about 3 minutes.
3. Add the garlic and mushrooms to the skillet, stirring occasionally. Cook until the mushrooms are golden and have released their moisture, about 5-7 minutes.
4. Stir in the fresh spinach and cook until wilted, about 2 minutes.
5. Pour in the heavy cream, bringing the mixture to a gentle simmer. Stir in the Parmesan cheese until melted and smooth.
6. Add the cooked pasta to the skillet, tossing to coat evenly in the creamy sauce. Season with salt, black pepper, and red pepper flakes to taste.
7. Garnish with fresh parsley before serving warm.

As you stir the creamy sauce, let it remind you of the small joys in cooking—like the first time I successfully recreated Nonna Rosa’s marinara, this pasta is a triumph of simplicity and flavor.