1. Add tortellini in a large saucepan of plenty of salted boiling water and boil, uncovered, according to the packet instructions.
2. Meanwhile, melt the butter in a large frying pan and gently fry the onion. Add the spinach leaves and toss thoroughly. Add the nutmeg and season with salt and pepper to taste. Cook for a while, stirring constantly.
3. Drain the cooked tortellini and return to the saucepan. Stir in the fetta cheese, cream, parsley and fold in the cooked spinach. Serve with freshly grated parmesan.