Finely chop the mushrooms and onion; sauté the onion in butter, add the mushrooms, season with salt and a little pepper, and cook covered until soft.
Once the mushrooms have absorbed the butter, add the tomato paste, beef stock and parsley, and reduce for a few more minutes - this is the book's own 'fines herbes' mushroom ragout - then take off the heat.
Finely chop the veal liver and mix with the cooled mushroom ragout, add the salt, pepper, madeira, one egg and the crushed bay leaf.
Pound the mixture smooth in a mortar (or food processor), then press through a sieve for a creamy, smooth paste.
Spread the trimmed tenderloin thinly with the liver-mushroom paste, then lay a row of blanched cabbage leaves over it.
Brush the cabbage leaves with the beaten egg, then wrap the whole thing tightly in caul fat (or bacon slices, or foil).
Put fat underneath it in a roasting tin, and roast in a 200°C oven for about 30 minutes.
After roasting, rest it for 15 minutes in a warm place (switched-off oven with the door ajar).
Cut into thin slices, arrange on the platter so it looks like a whole roast again, and serve with the vegetables.
Based on: Malatinszky Fanny szakácskönyve (a classic Hungarian cookbook), modernised. Calories and protein are estimated.