Add bread cubes to large mixing bowl and top with heavy cream and grated onion (plus juices from grating the onion). Stir and let sit a minute or two. Mash with a fork.
Add beef, pork, egg, parsley, salt, pepper, nutmeg, and allspice. Mix well.
Use small cookie scoop to scoop out and roll into roughly 1 inch wide meatballs.
Add oil and butter to large skillet and heat over MED/MED-HIGH heat. Add meatballs, working in batches (about half at a time), and cook on all sides, until browned and mostly cooked through, about 5-7 minutes. Remove to a plate and repeat with remaining meatballs.
Drain off any excess oil but don’t wipe out the skillet.
Add butter to skillet and heat over MED heat. Once melted, whisk in flour and cook, stirring occasionally for 2 minutes.
Slowly add beef broth, whisking as you add it, until all broth is added. Whisk in Worcestershire sauce and bring to a simmer.
Once gravy is simmering, add all meatballs and simmer 5-7 minutes, until meatballs are cooked through and gravy has started to thicken.
Stir in heavy cream and simmer another 2-3 minutes, until gravy is a smooth and silky sauce that coats the back of a wooden spoon.
Serve over buttered cooked egg noodles or mashed potatoes and garnished with minced fresh parsley.
