In a large mixing bowl, combine the breadcrumbs with the milk, egg, onion, garlic, salt, pepper, and allspice. Let stand for 10 minutes.
Add the ground beef and pork to the breadcrumb mixture. Mix with your hands until combined.
Using a standard size cookie scoop, portion meat into balls. Roll in your hands to create a smooth, even ball. Set aside on a piece of parchment paper.
In a large nonstick skillet set over medium heat, add the butter and oil. Once hot, place the meatballs around the pan, leaving about a 1/4 of an inch between each meatball, more if possible.
Carefully fry the meatballs until golden brown on each side (ensuring that they are fully cooked throughout, a meat thermometer can help). Transfer to a paper towel-lined plate, set aside. Remove any large bits remaining in the pan with spoon.
In the same skillet, add the butter for the gravy. Once melted, add the flour and whisk until it turns golden brown. Slowly whisk in the chicken broth, and beef broth. Bring the mixture to a low simmer. Add the dijon, worcestershire, soy sauce, salt, and pepper. Whisk in the half and half. Let thicken for a minute.
Return the meatballs back to the pan and serve, or serve the meatballs alongside the gravy.