Authentic Dutch bitterballen featuring a velvety, rich slow-cooked beef ragout seasoned with nutmeg and parsley, rolled in crispy panko breadcrumbs and deep-fried to a shatteringly crisp golden sphere.
Melt the butter in a heavy saucepan over medium heat. Whisk in the flour and cook for 2 minutes to form a blond roux. Gradually pour in the cold beef stock in a steady stream, whisking constantly until a very thick, smooth sauce forms. Stir in the shredded beef, chopped parsley, nutmeg, salt, and pepper.
Spread the warm ragout into a shallow tray, press clingfilm directly onto the surface to prevent a skin from forming, and chill in the refrigerator for at least 3 hours (or overnight) until completely firm and pliable.
Scoop walnut-sized portions of the firm ragout and roll them between your palms into smooth 3cm balls. Set up three bowls: fine flour, beaten egg, and breadcrumbs. Roll each ball in flour, dip thoroughly in egg, and coat in breadcrumbs. Dip in egg and breadcrumbs a second time to ensure a leak-proof shell.
Heat sunflower oil in a deep fryer or deep heavy pot to 180°C. Fry the bitterballen in small batches for 3 to 4 minutes until deep golden and crispy. Drain on kitchen paper and serve piping hot with sharp mustard.