Begin by finely chopping the medium onion and gather all your ingredients: ground beef, breadcrumbs, eggs, mustard, salt, and pepper.

In a large mixing bowl, combine the ground beef, chopped onions, breadcrumbs, eggs, Dijon mustard, and salt and pepper. Mix thoroughly for 2 to 3 minutes until well-combined.

Wet your hands with water and shape the mixture into patties, approximately one inch thick. Place them on a plate.

Heat a large skillet over medium heat, add oil, and cook the patties for 5 to 7 minutes on each side until golden brown and they reach 160°F.

Transfer the patties to a paper towel-lined plate to drain excess oil and let them rest for a few minutes.

Serve the Frikadellen with creamy mashed potatoes or in a toasted bun with mustard.