In a large mixing bowl, combine ground beef, breadcrumbs, egg, milk, finely chopped onion, allspice, Worcestershire sauce, salt, and pepper. Mix until well combined and form into small meatballs.

Heat a large skillet over medium heat and add oil. Once hot, add the meatballs and sear for 8-10 minutes until browned and cooked through. Transfer to a plate.

In a large pot, bring salted water to a boil and cook pasta according to package instructions, about 10-12 minutes, until al dente. Drain and set aside.

In the same skillet, add oil and sauté onions until translucent, about 3-4 minutes. Stir in cream of mushroom soup and beef broth, simmer for a few minutes, adjusting seasoning as needed.

Preheat your oven to 375°F (190°C). Combine cooked pasta and meatball sauce in a large mixing bowl, then transfer to a greased baking dish. Top with cheese if desired.

Bake in preheated oven for 20-25 minutes until bubbling and lightly golden on top. If topped with cheese, it should be melted and starting to brown.

Let the casserole cool for about 10 minutes before serving. Enjoy your heartwarming meal!