01 - Bring a large pot of salted water to a boil. Cook the pasta according to package instructions until al dente. Reserve 1/2 cup of cooking water, then drain the pasta.
02 - While the pasta cooks, heat olive oil and butter in a large skillet over medium heat. Add the onion and sauté for 2–3 minutes until translucent.
03 - Add the minced garlic and cook for 1 minute, stirring frequently until fragrant.
04 - Add the spinach and a pinch of salt. Cook, stirring, until the spinach wilts (about 2–3 minutes).
05 - Reduce heat to low. Pour in the heavy cream and stir in the Parmesan cheese. Add nutmeg if using. Simmer gently for 2–3 minutes until the sauce thickens slightly.
06 - Add the drained pasta to the skillet, tossing to coat in the sauce. If needed, add a little reserved pasta water to reach desired sauciness. Season with salt and freshly ground black pepper to taste. Serve immediately, garnished with extra Parmesan if desired.