In a Dutch oven, cook meat and onion over medium heat until meat is no longer pink; drain. Add the tomato sauce, tomatoes, mushrooms, parsley and seasonings. Bring to a boil. Reduce heat; cover and simmer for 45 minutes, stirring occasionally.
Uncover; simmer 15 minutes longer or until sauce reaches desired consistency. Discard bay leaves. Freeze in meal-size portions.
To use frozen meat sauce: Thaw in the refrigerator overnight. Place in a saucepan; heat through.