Pound the top round slices with a meat mallet, so they're thinner and more tender.
Heat the lard in a pot, add the finely chopped onion, and fry over medium heat until translucent.
Add the meat, and brown it on all sides for a few minutes.
Season with salt and pepper.
Pour in a little beef stock, cover, and braise over low heat for 1-1.5 hours, until the meat is completely tender - check occasionally and add more stock if needed.
Once the meat is tender, if there's still a lot of liquid left, reduce uncovered to the desired thickness.
Top each portion with a spoonful of sour cream when serving.
Based on: Malatinszky Fanny szakácskönyve (a classic Hungarian cookbook), modernised. Calories and protein are estimated.