In a large bowl, combine the minced beef, beaten eggs, chopped onion, melted clarified butter, hot mustard, salt, and pepper. Knead together until just combined.
Shape the mixture into equal patties of approximately 100 g each. Place on a baking sheet and freeze for 3 hours.
Heat a large skillet over medium-high heat.
Add the frozen patties and fry for 2-3 minutes on each side until golden brown.
Reduce heat to medium and continue cooking for 8-10 minutes until the internal temperature reaches 71 °C (160 °F).