In a saucepan, melt the butter over medium heat. Add the flour and cook, stirring constantly, for about 2 minutes until it forms a roux.
Gradually whisk in the beef broth and heavy cream. Continue to cook, stirring constantly, until the mixture thickens and becomes smooth.
Add the shredded meat, Dijon mustard, nutmeg, black pepper, and salt. Mix well and cook for a few more minutes.
Remove from heat and stir in the chopped parsley if using. Let the mixture cool completely. Once cooled, refrigerate for at least 1-2 hours to firm up.
Once the filling is firm, shape it into small balls, about 1 inch in diameter.
Prepare three shallow dishes: one with flour, one with beaten eggs, and one with breadcrumbs.
Roll each ball in the flour, then dip into the beaten eggs, and finally coat with breadcrumbs. Ensure each ball is fully coated.
Heat vegetable oil in a deep fryer or large saucepan to 350°F (175°C).
Fry the bitterballen in batches until they are golden brown and crispy, about 3-4 minutes.
Remove with a slotted spoon and drain on paper towels.
Enjoy your meal!