Cook pasta according to package directions and reserve some of the cooking water.
Heat a medium skillet over medium heat. Add olive oil, butter, garlic and nutmeg. Once the butter has melted add the spinach. Cook for 5 minutes, or until wilted. Season the spinach with salt and pepper to taste.
Add the cream, mascarpone and a ladle full of cooking water to the skillet. Simmer and then add more salt and pepper if needed.
Stir the drained pasta into the spinach sauce. Add the parmesan and toss to coat. Add more cooking water if needed, making sure the sauce is a silky consistency. Check once more for seasoning and serve.