How to make
Form the beef fillet into a thin sheet - use a knife, if necessary. Sprinkle with salt and pepper and gently tenderize the meat.
Dissolve the beef stock with 1 cup of cold water and let sit for 1 hour straight in the oven dish in which you'll be baking.
Then, coat its surface with the finely chopped onion, mushrooms and chopped walnuts.
Roll it up and coat with plenty of oil. Cover the oven dish with foil and put it to bake for about 1 hour and 45 minutes, in a preheated 430°F (220 °C) oven.
Serve with a side of baked or boiled potatoes.
