In a large mixing bowl, combine breadcrumbs and milk. Let stand for 5 minutes to allow breadcrumbs to absorb the milk.

Add ground beef, ground pork, beaten egg, grated onion, nutmeg, allspice, salt, and pepper to the breadcrumb mixture. Mix gently with your hands until just combined (avoid overmixing to keep meatballs tender).

With slightly damp hands, shape the mixture into 1-inch meatballs (about 24-28 meatballs total).

Heat olive oil in a large skillet over medium-high heat. Working in batches to avoid crowding, brown the meatballs on all sides, about 8-10 minutes per batch. The meatballs don't need to be fully cooked through at this point.

Transfer browned meatballs to a plate and set aside. Pour off all but 1 tablespoon of the drippings from the skillet.

In the same skillet, melt the butter over medium heat. Whisk in flour and cook for 1-2 minutes, stirring constantly until it turns light golden brown.

Gradually whisk in beef broth, making sure to scrape up all the flavorful browned bits from the bottom of the pan. Bring to a simmer.

Add heavy cream, soy sauce, Dijon mustard, Worcestershire sauce, and dried thyme. Stir well to combine.

Return meatballs to the skillet and simmer in the gravy for 10-15 minutes until cooked through and the sauce has thickened.

Taste the gravy and adjust seasoning with salt and pepper as needed.

Garnish the meatballs with chopped fresh parsley and serve hot over mashed potatoes, egg noodles, or your favorite side.