Bring a pot of water to a boil. Add the ravioli and cook until slightly underdone, 8 to 9 minutes (the cook time will depend on the ravioli size).
Heat the butter and olive oil in a large skillet over medium-high heat. Add the sausage, nutmeg and onions and cook until the onions are translucent and the sausage is done, about 10 minutes. Remove the sausage and onions with a slotted spoon and set aside. Add the cooked ravioli to the pan and fry in the sausage fat (add 2 more tablespoons butter if the pan is dry) until golden, 3 to 5 minutes. Add the onion-sausage mixture back in along with the sour cream and cook for 2 minutes. Finish with parsley and serve immediately.