In a large bowl combine ground beef, ground pork, panko breadcrumbs, chopped parsley, allspice, nutmeg, grated onion, garlic powder, pepper, salt and egg. Using your hands, mix until combined.
Roll into 12 large meatballs or 18 smaller meatballs. In a large skillet heat olive oil and 1 tablespoon of the butter over medium high heat. Add the meatballs and cook turning continuously until brown on each side and cooked throughout. Remove the meatballs to a plate and keep warm.
Add the remaining 4 tablespoons of butter to the fond in the bottom of the pan and scrape the browned bits. This is where all of the flavor is hiding!
Add the flour to skillet and whisk until it turns brown and takes on a nutty aroma. Slowly stir in the beef broth and heavy cream. Bring to a gentle boil and add Worcestershire sauce and the Dijon mustard. Sauce will begin to thicken.
Taste the gravy to see if it needs salt or pepper. Return the meatballs and their juices to the gravy and simmer for 10 minutes or until the gravy is cooked to the consistency that you like it.
Serve over mashed potatoes, over egg noodles, or alongside my Crazy Good French Onion Noodle Casserole.