In a large skillet melt the butter over medium heat. When the butter has melted, add flour, a little at a time, whisking it until it transforms into a thick roux.
Slowly whisk in the beef broth. The roux should be smooth and velvety. Simmer the gravy for a few minutes then add parsley, onion, and ground beef. Stir then season with the salt, pepper and nutmeg.
Transfer the beef mixture to a container and refrigerate for several hours until the gravy has solidified. You can refrigerate overnight, but 3 or 4 hours will do.
Line 2 baking sheets with parchment paper. In a shallow bowl add the flour, in another bowl add the beaten eggs. Add bread crumbs to a small plate.
Shape the meat mixture into 1 inch meatballs. Place the balls on one of the prepared baking sheets.
Roll the balls first through flour, then eggs, then finally bread crumbs. Place these meatballs on the other prepared baking sheet. Once finished, place the baking sheet with the meatballs in the fridge until ready to deep fry.
In a large Dutch oven, wok or deep fryer, add vegetable oil. 2 inches of oil should suffice. Heat the oil to 375 F degrees.
Fry the bitterballen 6 at a time until golden brown, approximately 4 to 5 minutes. If you have enough oil in your fryer the meatballs will float to the top when fully cooked. Continue the process until all of the meatballs have been fried.
Serve hot with your favourite mustard for dipping.