In a large mixing bowl, combine ground beef, ground pork, breadcrumbs, egg, salt, pepper, allspice, and chopped onion. Mix until well combined.
Form the mixture into small meatballs, about 1 inch in diameter.
Heat a skillet over medium heat and add a bit of oil. Cook the meatballs in batches until browned on all sides and cooked through. Remove and set aside.
In the same skillet, melt butter and whisk in flour to create a roux. Cook for 1-2 minutes.
Gradually whisk in beef broth and heavy cream. Bring to a simmer and cook until thickened.
Return the meatballs to the skillet and coat with the gravy. Simmer for a few more minutes until heated through.