In a mixing bowl, combine ground beef, breadcrumbs, sautéed onion, milk, egg, allspice, nutmeg, and salt until evenly mixed. Form into small meatballs.

Heat a large skillet over medium heat. Add meatballs and sauté for 6-8 minutes, until browned on all sides and cooked through.

In a large pot, boil salted water. Add pasta and cook until al dente, about 8-10 minutes. Drain and toss with olive oil.

In the same skillet, melt butter. Whisk in flour to make a roux, then gradually add beef broth and heavy cream, whisking constantly until thickened.

In a large baking dish, mix cooked pasta, meatballs, and creamy sauce until well coated.

Preheat oven to 350°F (175°C). Cover and bake for 30 minutes, then remove foil and bake for an additional 15 minutes.