In a medium sized bowl combine ground beef, panko, parsley, allspice, nutmeg, onion, garlic powder, pepper, salt and egg. Mix until combined.
Roll into 8 large meatballs or 16 small meatballs. In a large skillet heat olive oil and 1 Tablespoon butter. Add the meatballs and cook turning continuously until brown on each side and cooked throughout. Transfer to a plate and cover with foil.
Add 4 Tablespoons butter and flour to skillet and whisk until it turns brown. Slowly stir in beef broth and heavy cream. Add worchestershire sauce and dijon mustard and bring to a simmer until sauce starts to thicken. Salt and pepper to taste.
Add the meatballs back to the skillet and simmer for another 1-2 minutes. Serve over egg noodles or rice.