Finely chop the onion, coarsely grate the cheese and knead both with the other ingredients to form a mass. Adjust the consistency with approx. 3 tablespoons of breadcrumbs, the mass should be easy to shape.
Shape approx. 8-10 meatballs with your hands. Fry on both sides in hot oil in a pan. Then let it steep for about 10 minutes over low heat with the lid closed.
Tip: The whole thing also works with Gouda, but mountain cheese gives it a more intense taste.