Prepare the onions and garlic: Heat half of the olive oil in a large skillet over medium heat. Add the diced onions and minced garlic and cook until softened (about 5 minutes). Set aside to cool.
½ cup yellow onion, 2 cloves garlic
Mix the meatball ingredients: In a large bowl, combine the breadcrumbs, Parmesan cheese, egg, milk, onions/garlic, salt, oregano, allspice, nutmeg, and pepper. Let it sit for 5 minutes, then add the ground beef and pork. Mix gently—don't overwork the meat mixture.
½ cup yellow onion, 2 cloves garlic, ½ cup panko breadcrumbs, ¼ cup parmesan cheese, 1 large egg, ¼ cup milk, 1 teaspoon salt, ½ teaspoon oregano, ¼ teaspoon allspice, ⅛ teaspoon ground nutmeg, 1 pound ground beef, ½ pound ground pork, ¼ teaspoon pepper
Roll the meatballs: Shape the mixture into 1½-inch meatballs and place them on a plate. Chill them in the fridge for at least 15 minutes.
Make the broth mixture: While the meatballs chill, combine beef broth, Worcestershire sauce, mustard powder, and parsley in a measuring cup. Set aside.
2 ½ cups beef broth, 2 teaspoons Worcestershire sauce, 1 teaspoon mustard powder, 1 teaspoon parsley
Brown the meatballs: Heat the remaining olive oil in the skillet over medium-high heat. Brown the meatballs in batches, cooking about 1 minute per side. Remove and set aside.
2 tablespoons olive oil
Make the sauce: In the same skillet, melt the butter. Stir in the flour and cook for 2 minutes until it browns slightly.
4 tablespoons butter, 4 tablespoons flour
Add the broth and cream: Gradually pour in the beef broth mixture, stirring continuously. Bring to a boil, then reduce to a simmer. Stir in the heavy cream and adjust the seasoning.
½ cup heavy cream
Simmer the meatballs: Return the meatballs to the skillet, spooning sauce over them. Cook for 10-15 minutes on low heat until the meatballs are fully cooked.
Garnish and serve: Garnish with fresh parsley and serve over mashed potatoes, egg noodles, or your favorite side.