Combine the bread crumbs and the milk in a small bowl. Mix well, until the liquid is absorbed.
Add ground beef, ground pork, bread crumb mixture, and all remaining ingredients (except the butter and olive oil) to a large bowl and mix until combined well.
Pinch off about 1-2 tablespoons of meat, and form it into a ball. The meat should be a little smaller than golf ball size. Set the meatball aside on a parchment lined sheet. Continue rolling the meatballs until the meat is gone.
Heat up a cast iron skillet over medium heat on the stove. Add the butter and olive oil to the skillet.
Place meatballs in the skillet, and leave about an inch of room in between each one (do not overcrowd the pan). Cook the meatballs for about 2 minutes per side.
Once the meatballs are browned on each side, remove them and set aside on a cooling rack or bed of paper towels to drain excess grease. Continue cooking the meatballs in batches until they are all done.
Gravy
Using the same skillet (do not rinse or clean it out), add the butter. ONLY add the olive oil if there is not much grease left over from the meatballs.
Gently begin to sift the flour into the oil/butter. Use a whisk to combine the flour with the oil. The flour should absorb most of the oil, and become sort of clumpy.
Begin to whisk in the beef broth continue whisking until the clumps from the flour are dissolved, and mixture is smooth.
Slowly pour the milk into the gravy, next add the remaining ingredients.
Continue whisking the gravy until it is combined well. If the sauce is too thick (use your own judgement here), add more beef broth- one tablespoon at a time.
Taste for seasoning, add more salt and/or pepper if desired.
Nestle the meatballs back into the gravy. Change the temperature to low, and cover and simmer the meatballs for 10 minutes.
Serve over noodles or rice.