In a large bowl, mix ground beef, ground pork, salt, pepper, onion, and parsley.
In a separate bowl, combine bread crumbs, milk, and egg.
Pour the breadcrumb mixture into the meat and mix by hand until just combined. Form into meatballs.
Cook the Meatballs:
In a large skillet, melt butter over medium heat. Add meatballs in batches and cook until browned on all sides and cooked through, about 20 minutes total. Transfer to a plate and tent to keep warm.
Make the Gravy:
In the same skillet, melt butter and whisk in flour. Cook for 1–2 minutes until golden. Slowly whisk in beef broth, then stir in sour cream, salt, and pepper. Simmer until thickened.
Combine and Serve:
Return meatballs to the skillet and coat with gravy. Serve warm over egg noodles or mashed potatoes. Garnish with extra parsley if desired.