Melt the butter in a medium saucepan over medium-low heat. Once melted, whisk in the 1/2 cup of flour and cook for 2 to 3 minutes until the mixture forms a smooth, pale paste.

Gradually pour in the beef broth, whisking constantly to prevent lumps. Continue to cook and stir for about 5 minutes until you have a very thick, smooth gravy.

Remove the saucepan from the heat and stir in the finely shredded beef, parsley, Dijon mustard, nutmeg, salt, and black pepper. Mix thoroughly until the meat is evenly distributed.

Transfer the thick beef mixture to a shallow dish, cover tightly with plastic wrap, and refrigerate for at least 3 hours, or until completely firm.

Once the mixture is fully chilled, scoop out small portions and roll them into 1-inch balls using your hands. Place the formed balls on a parchment-lined baking sheet.

Set up a breading station with three shallow bowls: one with the remaining 1 cup of flour, one with the beaten eggs, and one with the breadcrumbs.

Roll each ball first in the flour, shaking off any excess, then dip into the beaten eggs, and finally coat thoroughly in the breadcrumbs until completely covered.

Heat the vegetable oil in a deep fryer or heavy-bottomed pot to 350°F (175°C). Fry the bitterballen in batches of 5 or 6 for 3 to 4 minutes, until they are deep golden brown and crispy.

Use a slotted spoon to carefully remove the bitterballen and let them drain on a plate lined with paper towels. Serve immediately with a side of whole grain or Dijon mustard for dipping.