In a large bowl, mix breadcrumbs, Parmesan, egg, and milk until well combined. Stir in onion, garlic, and spices like nutmeg and allspice. Finally, add the beef and pork, folding gently until everything is evenly combined. Don’t overmix—this keeps the meatballs soft.
Roll the mixture into 1.5-inch balls, using slightly wet hands to keep them smooth. Place them on a plate and chill in the fridge for about 15 minutes. This step helps them stay together while cooking.
Heat a little oil in your skillet over medium heat. Cook the meatballs in batches until each side is golden brown. Set them aside on a plate. The browned bits left in the pan will add extra flavor to your sauce.
In the same skillet, melt butter and whisk in flour until golden and nutty. Slowly add the beef broth while whisking to prevent lumps. Stir in Worcestershire sauce, Dijon mustard, and bouillon. Simmer until slightly thickened.
Temper the sour cream by mixing it with a spoonful of warm gravy, then whisk it back into the sauce. Add the meatballs, spoon sauce over them, and let everything simmer for about 10–15 minutes. Finish with chopped parsley before serving.