Soak bread in milk for about 5 minutes. Cook onion in 1 tablespoon of butter until tender. Mix meats, crumb mixture, onion, egg, parsley, salt, pepper, ginger, and nutmeg. Mix until well combined. Chill mixture. Wet hands and shape into 1 1/2-inch balls. Brown meatballs in 2 tablespoons of butter. Remove from pan. To make gravy, melt 2 tablespoons butter in pan with drippings. Stir in 2 tablespoons flour. Add 1 1/4 cups beef stock. Cook and stir until gravy thickens and bubbles. Return meatballs to pan with gravy and cook on low, covered, for about 30 minutes, basting occasionally.