Sauté the onions and garlic: Heat half the olive oil in a large skillet over medium heat. Add the diced onions and minced garlic, cooking until softened (about 5 minutes). Set aside to cool.
2 tablespoons olive oil, ½ cup yellow onion, 2 cloves garlic
Mix the meatball ingredients: In a large bowl, combine breadcrumbs, Parmesan, egg, milk, cooked onions and garlic, salt, oregano, allspice, nutmeg, and pepper. Let the mixture sit for 5 minutes, then gently mix in the ground beef and pork—don't overwork it.
½ cup yellow onion, 2 cloves garlic, ½ cup panko breadcrumbs, ¼ cup parmesan cheese, 1 large egg, 1 teaspoon salt, ½ teaspoon oregano, ¼ teaspoon allspice, ⅛ teaspoon ground nutmeg, ¼ teaspoon pepper, 1 pound ground beef, ½ pound ground pork, ¼ cup milk
Shape the meatballs: Roll the mixture into 1½-inch meatballs and place them on a plate. Chill in the fridge for at least 15 minutes to help them hold their shape.
Prepare the broth mixture: While the meatballs chill, mix 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, 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 slightly browned.
4 tablespoons butter, 4 tablespoons flour
Add the broth and cream: Slowly pour in the broth mixture while stirring continuously. Bring to a boil, then lower the heat 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 the sauce over them. Let them cook on low heat for 10-15 minutes until fully cooked.
Garnish and serve: Sprinkle with fresh parsley and serve over mashed potatoes, egg noodles, or your favorite side.