Mushroom Alfredo Pasta

Name: Mushroom Alfredo Pasta
Cuisine: European, Italian, Mediterranean
Ingredients: 250 g/8 oz pasta ((fettuccine or penne are recommended)); 1/4 cup (56 g/2 oz) unsalted butter; 1 small onion (, finely diced); 3 cloves garlic (, minced); 300-400 g mushrooms ((portabella, cremini, champignon), thinly sliced); salt and ground black pepper (, to taste); 1 1/2 cups (360 ml) heavy cream or half and half; pinch of nutmeg (, ground or freshly grated); 1/4 – 1/2 cup grated parmesan; 2 tablespoons chopped fresh parsley leaves or chives (, for garnish, optional)