Heat ½ of the olive oil in a large, high-walled skillet over medium heat. Add the finely diced onions and garlic. Soften for 5 minutes. Set aside and let cool.

In a large bowl, combine the breadcrumbs, Parmesan cheese, whisked egg, milk, cooled onions/garlic, salt, oregano, allspice, nutmeg, and pepper. Gently incorporate the meat until evenly combined, but without overworking it.

Roll into 1 ½-inch meatballs and place on a plate. Transfer to the fridge and let them chill for 15 minutes or up to overnight.

While the meatballs chill, combine the beef broth, chicken bouillon, Worcestershire sauce, Dijon, and parsley in a large measuring cup. Set aside.

Heat remaining olive oil in a large skillet over medium-high heat. Brown the meatballs in batches, brown for about 1 minute per side. Remove and set aside.

Melt the butter in the same skillet over medium heat. Stir in the flour and cook for 2 minutes until it begins to brown.

Add the beef broth mixture in small splashes, stirring continuously. Bring to a boil, then reduce to a simmer.

Place the sour cream in a medium bowl. Spoon some of the sauce into the bowl and stir until well-combined. Stir it into the sauce over low heat until incorporated.

Add the meatballs back to the skillet along with any juices from the plate. Spoon the sauce on top and heat through for 10-15 minutes.