Trim the thin outer membrane from the leg of rabbit or venison, then lard it with bacon strips using a larding needle.
Put the diced vegetables (carrot, parsley root, onion), whole peppercorns and a few bacon slices in the bottom of a pot, then lay the leg on top.
Season with salt, drizzle over the lemon juice, sprinkle with the finely chopped truffle, and pour in the red wine and a tablespoon of meat stock.
Cover and simmer over low heat for about 1 hour, making sure there's always liquid underneath - top up with a little stock if it cooks away.
Remove the lid, and place in a 180°C oven, stirring in a pinch of meat extract; continue roasting for 30-40 minutes, until the juices reduce to a nice thick consistency.
Once the juices have almost completely reduced, sprinkle with a tablespoon of flour, and return to the oven for a few more minutes.
Pour in enough stock to make a saucy consistency, then push through a sieve.
Stir sour cream into the strained sauce, bring to a boil, and season with salt to taste.
Slice the leg or place it whole on a platter, spoon over the sauce, and serve with puff pastry.
Based on: Malatinszky Fanny szakácskönyve (a classic Hungarian cookbook), modernised. Calories and protein are estimated.