Heat a large skillet over medium-high heat. Cook and stir beef in the hot skillet until browned and crumbly, 5 to 7 minutes. Drain and discard grease.
Combine cornstarch, salt, parsley, garlic powder, and onion powder in a small bowl.
Pour cornstarch mixture, milk, beef stock, and egg noodles into the skillet of beef. Bring to a boil. Cover and reduce heat. Simmer, stirring occasionally, until noodles are tender, about 5 minutes. Stir in sour cream and Parmesan cheese; do not return to a boil.