In a medium sauce pan, combine 2 cups water,onion, soup powder, salt and pepper. Bring to a boil. In a small bowl, stir cornstarch with 1/4 cup water. Pour into boiling liquid. Stir until thickened. Stir in mushrooms, cream of mushroom soup, parsley, paprika and sour cream. If it gets too thick, add more water.
Pour mixture over meatballs (bought or homemade). Cover and bake for 350 degrees for 25 to 30 minutes until heated through.
**Note** I use frozen meatballs ( bags) I get at the grocery store and thaw them. You can also use a large pot and warm meatballs on top of stove in sauce.