Prepared in 15 minutes or less.
In a large bowl, combine beef, egg yolks, onion, salt and fresh pepper. Mix well.
Form into round patties making a small center indentation. Place a touch of butter inside and cover with meat.
Grill patties according to desired meat temperature.
**You can substitute Swiss, Blue or Cheddar cheese for butter. Enjoy with Thai-Breaker Mayonnaise, lettuce and sliced beefsteak tomato on a toasted sesame bun. Serves 4.