Remove the skin from the onion, halve and cut into thin slices. Pat the meat slices a little tenderly flat. Score the outer top edge of the fat [1] in centimeter increments and season with pepper and salt. Heat half of the oil in a large frying pan and sear the meat slices on both sides for about two minutes (but they should still be pink in the middle). Remove the meat from the frying pan and keep warm.
Add the rest of the oil to the pan and fry the onion until golden brown. Season with salt.
Remove the onion from the frying pan, place it on the meat slices and keep warm. Put the frying pan back on the fire while it is still hot and extinguish the drippings with red wine. Add the butter to the boiling wine until it melts and season the sauce.
In the meantime, remove the peel from the potatoes and slice them finely. (A cucumber slicer can be used for this purpose.) In a coated frying pan, or even better an iron pan, heat clarified butter and toss the potato slices in it until just golden brown (if browned too long, the fried potatoes will become dry and hard). Season with salt.
Arrange meat with onions, add sauce and serve with fried potatoes.
[1] The Beiried tastes better with fat edge. If you don’t like it, you should still roast with fat edge, and cut away the edge only after roasting. The geri