First prepare the meatballs. Sauté the onion and garlic with salt and pepper in a hot oiled frying pan for about 5 minutes until soft and lightly colored, adding the chile flakes after a minute or two. Place the beef in a large bowl and season with salt and pepper. Put the breadcrumbs in a separate bowl and moisten with the milk. Season with salt and pepper, then stir the breadcrumbs and onion mixture into the beef and combine well. With wet hands, shape the beef mixture into large balls about 1½ inches wide. Transfer to a lightly greased plate or baking sheet and chill for 30 minutes until firm.