In a mixing bowl, combine ground beef, egg, breadcrumbs, milk, salt, pepper, and allspice. Mix well and form into small meatballs.
In a large pot, melt butter over medium heat. Add chopped onion and cook until softened.
Add meatballs to the pot and cook until browned on all sides.
Sprinkle flour over the meatballs and stir to coat. Cook for another minute.
Gradually add beef broth, stirring constantly. Bring to a simmer.
Add heavy cream, Worcestershire sauce, and Dijon mustard. Stir well and simmer for 20-25 minutes, until the meatballs are cooked through and the stew has thickened.
Season with salt and pepper to taste. Serve hot.
Notes:
Serve with mashed potatoes or over egg noodles for a complete meal.