Preheat oven to 350 degrees F (175 degrees C). Lightly grease a 9x13 inch baking dish.
In a large bowl, combine ground beef, ground pork, chopped onion, bread crumbs, egg, and milk. Season with parsley, Worcestershire sauce, 2 teaspoons salt, and 1 teaspoon pepper. Mix well with your hands. Shape into walnut-size balls, and place on baking dish.
Bake for 30 minutes in preheated oven. Turn frequently so they brown evenly on all sides.
To make the sauce: In a saucepan, combine oil, flour, paprika, 1 tablespoon salt, and 1 teaspoon pepper. Cook over medium heat until sizzling. Stir in hot water and sour cream until smooth and heated through.
When meatballs have cooked 30 minutes, pour sauce over the top, and return to the oven for 20 minutes, stirring occasionally.