Wash the prune, fill it with boiling water and leave to swell.
Incision in the meat side, and deploy in the form of book.
Mix sour cream, mustard and salt.
Next, rub the meat in two-thirds of the mixture.
Chop the prune in a blender.
Put it on the meat and turn in the roll.
Spread the top with walnuts and rest of mixture.
Place on foil. Lift edges of foil over the roll.
Heat up the oven to 200c.
Spread baking tray with oil and place roll on it.
Cook 60 min.
For a quarter of an hour before the roll is ready,
open the foil and bake until a golden brown.