Make the meat mixture. In a large bowl, combine the ground beef, beaten egg, chopped onion, minced garlic, panko breadcrumbs, nutmeg, 1 tablespoon of the parsley (reserve the rest), salt, and pepper.
Make about 20 meatballs and brown them in a large skillet with olive oil over medium-high heat, turning occasionally, until all sides are golden brown — this step adds deep flavor to both the meatballs and the sauce. You may have to do this in batches. Don’t worry if they are not fully cooked at this time — they’ll finish cooking to a safe internal temperature of 165°F. Transfer the meatballs to a plate.
Make the sauce: To the same skillet, add the beef broth, condensed cream of chicken soup, sour cream, and the remaining tablespoon of parsley. Stir well to combine, then bring to a gentle boil, stirring occasionally until the sauce is smooth and slightly thickened. Once slightly thickened, reduce the heat and simmer for 2 minutes to blend the flavors before adding the meatballs. If the sauce thickens too much, add a splash of broth or milk to loosen it before serving. Taste the sauce before seasoning — you may not need extra salt, as the soup already adds plenty of flavor.
Transfer the meatballs back to the skillet and simmer, covered, for 5–7 minutes, or until the meatballs are fully cooked and reach an internal temperature of 165°F.
Serve hot over your choice of cooked egg noodles, mashed potatoes, or rice. Garnish with extra parsley or a dash of black pepper for a polished finish.