Prepare the Meatballs: In a large bowl, combine the ground beef, ground pork, breadcrumbs, milk, egg, onion, garlic, salt, pepper, parsley, and nutmeg. Mix until well combined but do not overwork the meat.
Shape the Meatballs: Form the meat mixture into small balls (about 1 1/2 inches in diameter). Set aside on a plate.
Cook the Meatballs: In a large skillet, melt 2 tablespoons of butter over medium heat. Add the meatballs in batches, frying them until browned on all sides, about 6-8 minutes. Remove from the skillet and set aside.
Make the Mashed Potatoes: Peel and chop the potatoes into chunks. Boil them in salted water for 15-20 minutes, until tender. Drain and mash the potatoes. Stir in the butter, cream, salt, and pepper until smooth.
Prepare the Gravy: In the same skillet used for the meatballs, melt 2 tablespoons of butter. Stir in the flour and cook for 1-2 minutes. Gradually whisk in the broth, followed by the cream. Simmer until thickened, about 5 minutes. Season with salt and pepper to taste.
Assemble the Dish: Serve the meatballs over the mashed potatoes, generously drizzling with gravy. Optionally, garnish with fresh parsley.