Season the tenderloin medallions with salt and pepper.
Heat the fat in a pan over high heat, and fry the medallions 2-3 minutes per side, until the desired doneness (medium-rare) is reached, then take them out and rest, covered with foil.
In the same (or another) pan, with a little fat, fry the goose liver slices over very high heat for only 30-60 seconds per side, as they melt quickly - season lightly with salt.
Take out the goose liver, and keep it warm.
Sprinkle a pinch of flour into the pan the meat was cooked in, fry for a minute, then pour in the madeira, bring to the boil, and scrape up the browned bits from the bottom of the pan.
Pour in the beef stock, and simmer over medium heat for 3-4 minutes, until it reduces to a syrupy sauce; if you like, finish it with a knob of cold butter for shine.
Place a slice of goose liver on each tenderloin medallion, pour over the madeira pan sauce, and serve immediately.
Based on: Malatinszky Fanny szakácskönyve (a classic Hungarian cookbook), modernised. Calories and protein are estimated.