Prepare the Onion and Garlic: Heat 1 tablespoon olive oil in a skillet over medium heat. Add diced onion and cook for 3–4 minutes until softened. Stir in minced garlic and cook for another minute. Let cool.
Mix the Meatball Ingredients: In a bowl, combine panko, Parmesan, egg, milk, salt, oregano, allspice, nutmeg, and pepper. Add the cooled onion mixture, ground beef, and ground pork. Mix until just combined.
Shape and Brown the Meatballs: Form into 1-inch meatballs. Heat the remaining tablespoon of olive oil in the skillet and brown the meatballs on all sides. Set aside.
Make the Sauce Base: Melt butter in the same skillet over medium heat. Whisk in flour to form a roux, cooking for 1–2 minutes. Gradually add beef broth, whisking continuously. Stir in the bouillon cube, Worcestershire sauce, Dijon mustard, and parsley.
Simmer and Finish the Sauce: Simmer for 3–5 minutes to thicken. Reduce heat and stir in sour cream.
Cook the Meatballs in the Sauce: Return meatballs to the skillet, cover, and cook on low for 10–12 minutes, until fully cooked.
Serve: Serve over egg noodles, mashed potatoes, or rice. Garnish with parsley if desired.