Stir the dairy free breadcrumbs and dairy free milk together in a large bowl. Let them stand for 5 minutes until softened.
Add the beef, pork, egg, grated onion, salt, pepper, allspice, and nutmeg. Mix gently until just combined, then shape into 24 meatballs.
Heat the olive oil in a large skillet over medium heat. Brown the meatballs in batches for 6 to 8 minutes, turning often, then transfer them to a plate.
Melt the dairy free butter in the same skillet. Whisk in the flour and cook for 1 minute.
Gradually whisk in the beef broth, then the dairy free milk. Stir in the Worcestershire sauce, Dijon mustard, salt, and pepper.
Return the meatballs and any accumulated juices to the skillet. Simmer for 8 to 10 minutes, turning the meatballs once, until cooked through and the sauce is thick and smooth.
Garnish with parsley and serve over mashed potatoes, buttered dairy free noodles, or rice.