01 - Cook the pasta in a large pot of salted boiling water according to package instructions until al dente. Drain the pasta, reserving 1/2 cup of the pasta cooking water.
02 - While the pasta cooks, heat olive oil and butter in a large skillet over medium heat. Add the finely chopped onion and sauté for 2 to 3 minutes until softened.
03 - Stir in the minced garlic and cook for 1 minute more until fragrant, being careful not to burn it.
04 - Add the fresh baby spinach to the skillet and cook, stirring frequently, until the spinach has completely wilted, approximately 2 to 3 minutes.
05 - Pour in the heavy cream and bring the mixture to a gentle simmer. Stir in the grated Parmesan cheese and ground nutmeg. Continue to simmer for 2 to 3 minutes until the sauce begins to thicken slightly.
06 - Add the drained pasta to the skillet with the sauce. Toss thoroughly to combine, adding the reserved pasta cooking water as needed to achieve the desired sauce consistency.
07 - Season the pasta dish with salt and freshly ground black pepper to taste. Serve immediately, garnished with extra Parmesan and a sprinkle of black pepper.